I agree with you to an extent, but I will note that while most Americans don't directly use Twitter, I think a much much larger fraction are exposed to it. It's hard to escape when every news outlet and gossip farm cites it constantly and you have to factor that in when discussing its relevance.

I simultaneously don't think I personally know a single person that uses Twitter regularly and yet I equally don't think I know a single person that doesn't know what it is and sees second hand content from it regularly.