Automatically creating a shadow account for everyone on Instagram?
Even allowing people to follow that account?
Sounds like they really wanted to push Threads out the door in a big way.
If you look carefully at Meta's actions in the last few years, you'll notice they're slowly stepping away from the Facebook brand and product. I suspect that they no longer internally consider Facebook to be their main product, giving way for Instagram, which at the moment is a lot more popular and despite the obvious association doesn't have a tainted name the same way Facebook does.