remember back in the day when drug testing busted people for drugs because of poppy seeds (as on bagels)
Did this actually happen?
Occasionally, it seems. It’s usually a matter of dispute because the “poppy seed bagel defense” is such a well-known excuse, it’s probably been used by people who are not always entirely on the up and up. But in cases like the above it does seem more a matter of an idiot organization using an insensitive test and then not following up properly before calling the authorities.
ETA: Yet another feather in the cap of our fine American healthcare system 
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I can’t speak to poppy seeds specifically but back in the day (early '80s) my future wife was a lawyer in USAF. Drug testing was new then and the official position was that a) drug tests are infallible, b) the sample custody procedures are perfect, so c) all positive test results are absolute proof of guilt so punishment or dismissal from the service was practically instant and practically automatic after a brief kangaroo hearing. Which made her job as the designated defense attorney very very difficult.
There was quite a fight by both the legal and medical establishment to convince the brass that both (a) & (b) assumptions are false, especially at DoD’s scale. By the time she left the service a few years later things had smartened up a bunch. Custody procedures were much better, split samples were required, all positive tests had MRO review, and there was an acknowledged list of legit foods and medications that triggered false positives, etc., etc.
But the big difference was getting the brass to alter their hidebound ideas about (c). I suspect there are still cockamamie organizations that think the same way today: a positive test is proof of something bad and we don’t want any of that around our company. Probably mostly due to a misplaced fear of some nebulous legal liability attaching to the company if that employee was later involved in a problem.
And totally missing the concern they should have about the legal liability the company will have for wrongful termination.