I might be pretty ignorant here but what is so proprietary about Twitter/Threads? It just lets people make public status updates and share photos. Unless they literally used the same lines of code, how is it infringement and trade secrets?
It's really not. Not to mention, like someone else said, Meta has said that they don't even have any former Twitter employees on their engineering team for Threads.
It's easy to make a website that lets random users post whatever they want and then display it in a feed. You could teach a novice how to do it in a weekend. Building a site that can scale to millions of users pretty much overnight is where the secret sauce is.