you’re not supposed to just eat it straight from your hand.

Eating customs are a hit different than just actually ingesting a bottle of laxative. Eating customs also aren't stated on a product.

Whereas this is clearly labeled "magnesium citrate". My point being that while some American kids might not pay attention to what it says on the label, it'd make sense that a foreign exchange student would read the label and know what magnesium citrate is, or at least realise it's medicine of some sorts. Seeing as they're students, in an exchange program, they probably know the language somewhat.

So I standby what I said.

Your example is more akin to eating pizza with a knife and fork in Italy rather than chugging a bottle of laxative by accident.