Notice how it only says that Threads posts will be shared on the fediverse. It says nothing about fediverse posts showing up in Threads. This is meta allowing its users to spam the fediverse. It's a hostile, egotistical feature with no sense of community.
They have published a roadmap, which says it will be fully bidirectional by the end of the year. So far they have followed that roadmap, and I don't see a reason why they would stop doing that.
As somebody who used to publish to FB by subscribing my FB account to RSS feeds so that the posts from those feeds would show up on my "wall", I am highly skeptical in the long term interoperability of anything FB owned that directs content created outside the walled garden into the walled garden.
