Correct - They are behaviors that tend to be cultural - which do trend towards Nationality. Because it's BEHAVIOR that is normally acceptable/allowed to them... which is something that doesn't happen in isolation.
You ever watch Carnival in Rio? Or a South American football match? And you think there is no association at all between how these kids behave and where they come from?
Put down the PC cross - Stereotypes are not all evil. You can't possibly try to argue the observations about these groups doesn't happen and isn't real... nor that there isn't an association with where they are from.
Luckily for most WDW visitors, the domestic cheer groups are pretty condensed into when they visit the parks and generally are the only ones that even approach this level. The school trips, the band trips, the pop kids, etc etc etc don't have nearly the same disruptive behavior while in the parks. Nor are they are as prevalent and distinguishable.
None of these groups are being offended by being labeled or sterotyped as Brazilian. That's part of the mindset - to be proud of your heritage and traditions.