The point is that if you just see a kid on the street throwing a tantrum, you don't know which of those situations you're actually looking at

OP was referring to observations at friend's houses. Presumably they'd be aware of any underlying issues.

Judging random people on the street isn't wise. Judge your friends and loved ones instead! :D

I mean, do you even know the full story at a friend's house? I guess it depends on how closely you know them, and whether they've confided any developmental issues they're children are dealing with.