Fresh snow is fine. Most kids in snowy areas have fond memories of trying to catch a snowflake on their tongue. Likewise, fresh snow that hasn’t touched the ground is likewise normally fine. Maybe this person had been eating old, crusty snow. Even if that was white, I’d be a little leery of eating it because it has been sitting out long enough to collect some crap I wouldn’t want to eat.
More seriously, those of us who were raised in the snow belt had pretty much outgrown snow eating by the time we were four. The OP’s anecdote may reflect the feeling of the “locals” that grown-ups have no business doing such a childish thing.
Ever notice how clear the air is after a good rain?
First part of the rain is washing out much of the stuff in the air that is not air. Later ½ of the rain is much cleaner.
Snow that started as rain up higher ( most ) & snow that has been snow from way up high is doing the same. Second ½ rain & snow is about as clean as you can get without extra processing. IMO
YMMV
Recent thread about snow ice cream.
Midwest born and bred here. Were I to eat snow, I’d find some “top” fresh snow that appeared undisturbed by animal/human activity, far away from roads/walkways (to avoid plow/snowblower/shovel-tossed salt or sand), and carefully scoop it up to avoid anything gross in it that might be hidden.
My parents discouraged (but didn’t forbid) us from eating snow or sucking on icicles, but that’s at least partially because we did have a dog (and it’s hard to poop-scoop in winter sometimes, especially if your dog likes playing outside for extended times) and lived in an area with a lot of wildlife. We definitely heard “don’t eat the yellow snow!” early on.
The water that everybody drinks? Fish shit in it. Animals bleed and die in it. Humans swim in it. But you should be concerned about snow?
People get weird about the stupidest stuff.
Precious darlings skiing in the east should be tested for allergy to pseudomonas syringae INA proteins frequently used in man-made snow. If they eat snow crystals formed around these, then the water in their bodies will freeze up and they will suffer a fracture if they fall, for as we all know, precious darlings never fall because they are all such great skiers, so their broken bones must be someone else’s fault. Tell this to all the ski-parents you know.
OK, that’s all a bunch of shit – not the bacteria proteins, but rather the business about them harming children. Still, it can never hurt to give ski-parents something more to fuss over concerning their precious darlings, so please spread the woo. And with that, I’m off to go ski for the afternoon. Wheeee!
I was always taught that you never eat the first snow. I do not remember why.
Which the kids routinely ignore. And provided they have enough sense to avoid obviously contaminated snow, this typically leads to no effects worse than a cold mouth.
Thus do kids learn that the wisdom of adults has its limitations.
All the talk of yellow snow reminds me of an old joke:
*His Lordship, looking out of an upstairs window. “By jove Cynthia, young Dick has written his name in the snow.”
“Nothing wrong with that,” her ladyship replies. “I recall that you boasted of doing that yourself as a young man.”
“That may be, but this is in our daughter’s handwriting.”*
Snow is full of bacteria. None of the articles I’ve found say if the kind of bacteria(s?) in snow and rain will make you sick, though.
It’s not ripe.
While anything is possible, it’s good to remember that bacteria have preferred temperature and humidity needs, just like people. Generally speaking, things that thrive in a nice moist 37degree (C) environment like people will not be very prosperous in a dry cold environment like air. If one is taking bets, one should be more concerned with things in food (which may be at or around our body temperature within “the danger zone” or rooms which are warm and humid (like bathrooms) or in environments that humans touch frequently, like keyboards and elevator buttons. While there is indeed a huge biosphere of bacteria in the air, most of it won’t do well inside a hot sticky wet human body.
Spores and viruses are an entirely different kettle of germs, of course.
As others have already stated, nothing wrong about eating fresh snow, if not visible contaminated or old, unless you are in a already very polluted area.
I’ve done a lot of winter mountain skiing (not voluntarily I assure you, damn army!), and to cut down on weight we’d always bring as little water as possible, and melt snow, either over a fire (when we needed lots of water) or in a bottle placed inbetween layers of clothing (for drinking).
Whenever I drank from the bottle, I’d refill it with snow and allow this to melt using body heat. As long as you don’t put the bottle next to skin, this will not cause localized heatloss.
Eating snow directly, or drinking ice cold water, is a bad idea when not moving, as it will lower your core temp quite suddenly - which is not a good thing if you are trying to stay warm.
What I was told by my Mama (yeah, we get told not to eat snow as kids in Norway as well), is that old snow close to the ground could have worms in it, and therefore was bad for you. No idea if thats true, tough.
Not sure where you live, but around here we have water treatment plants. 
And some water treatment plants are almost as good as water that’s been distilled and recondensed.
If you use snow as your only source of water, as Mt. Everest climbers and polar researchers do, you’ll find that it tastes boring, and that you’ll need mineral supplements. For the occasional snow-eater, there’s nothing to fear. Whatever air pollutants the snow picked up, the amounts are tiny.
Yeah, I’m just saying that the “I don’t drink water; fish fuck in it” joke about water is cute (and old), but if you live in a first world country it’s almost assuredly not true unless something has gone wrong, because that stuff gets processed before you drink it. So no one’s willingly, intentionally drinking water that has significant levels of piss or rotting corpse in it and therefore making snow-eating seem quite sane in comparison.
(Again, I don’t think it’s insane, but I’d certainly make sure to find clean, untouched snow that’s not near roads/sidewalks.)
Do they treat wells and streams? No.
Snow looks nice and pure and clean and white. But… (of course) …I read somewhere…are there some kind of INSECTS that live and breed on top of that nice clean white snow? Here? In Antarctica? In the Arctic Circle?