Calvin’s done a number of things that have made other people physically ill. Like squashing his sandwich and banana into his thermos so he can “choke it down all at once, and it saves my teeth unnecessary wear and tear!” Susie has a priceless look of revulsion in panel 3, and in panel 4, has taken her own lunch and booked out. Or the time he needed something for show-and-tell, then sneezed and said, “Never mind; do we have any baggies?” (Mom: “I don’t want to know…I don’t want to know…I don’t want to know…”
Now, compare and contrast with Jason Fox, who once tied all his spaghetti strands into one long rope so he could suck them all down at once. “Cool—I can pull it back out!” Jason and Calvin have a similar “do it to see if it can be done” mentality, though Jason tends more towards actively trying to gross other people out, while Calvin is simply bewildered that others don’t share his, uh, “tastes”.
But I think it’s most likely that Calvin did something with noodles that made the other students, and possibly some teachers, so traumatized that ambulances had to be called.