It's an interesting strategy, the app on the Apple App Store is published by "Instagram Inc" rather than Meta, prominently named as "Threads, an Instagram App". They could have launched it as a completely separate brand, but that would have required marketing such as "the new app from Meta", and everyone more closely associates Meta with Facebook.
It's quite surprising they never launched a microblogging network before, but I suppose they have never really launched a new network, only ever acquired them... does that show that they feel threatened, have weakening market position, and need a new direction?