They obviously say 'Join X on Threads', although X has not signed up for Threads. Again, read the linked post. This is btw also what Meta is doing even if you don't have a Facebook, WA or any account in Meta's closed system. Someone posted an article, here for you again: https://www.newsweek.com/facebook-tracking-you-even-if-you-dont-have-account-888699
I end this conversation now. It should be very clear what point is here if one communicates in good faith, and I don't have the time to engage with Meta's PR writers (sorry, guys, but this is waste of time).
You claimed there are substantially more users than there actually are. Yet the article you provided is of a complete different topic.
And as many commentors have already said that those usernames are placeholers for their respective instagram users. Otherwise there would be a billion Threads users.
I called you out on your bullshit SO I am a Meta PR guy.