Pretty sure they’re not. I mean those are instagram accounts, but only those who enabled threads. It’s also at 93 million now.
Why is it so hard to believe that people download the app and try it out? It’s easy to do, users don’t have to create a new account, the app is number one on the App Store, they’re probably advertising it in instagram, and it’s still just 20% of the instagram userbase.
Decentralization is nice, but most people don’t care about it and it’s too complicated or annoying to sign up there. Threads is dead simple and people want a Twitter replacement. It’s also “just” a fifth of the Twitter userbase.