Knowledge is not automatically a trade secret. Skills from one job can be freely applied to another. The onus is on Twitter to prove that the employees took something specific (copyrighted code, a patented algorithm implementation, some other asset or IP) which is the property of Twitter and used it to build Threads. The last high profile lawsuit of this nature was Google vs Uber for stolen self driving tech, which had all of this and more.
Sorry if I was not clear, I'm saying that without hiring any Twitter folks, the Instagram folks could easily create a Twitter clone. Instagram posts & comments could be adapted pretty easily.
The question is whether the Twitter employees actually brought and used trade secrets for this effort.
The thing is these employees could have come in and directly used all the "knowledge and competency" they learned at Twitter to build Threads and it would still be 100% legal. There is a very high bar to proving whether any of it is actually a trade secret.
