Why do some Americans believe the diversity between US States is comparable to European countries?

A little over a week ago, this American girl on TikTok very loudly and very proudly proclaimed that US States were just as different between each other as European countries were between each other. To my surprise, some Americans either partly or fully agreed with her.

This same girl then went on to (again, very loudly) say that all of central Europe was the same and that in the Netherlands, Germany, Belgium and Luxembourg they all spoke the same language.

The main argument as to why US states are apparently as culturally diverse berween each other as European countries, is that the USA is big and US States are the size of European countries.

I guess I'm wondering why some Americans think the bigger a country is, the more diverse it must be. By that logic, both Canada, China and Russia would be more diverse than the USA since they're bigger countries. Am I missing something here, because I don't see the direct correlation between landmass and cultural diversity?