That's pretty likely, given how many have left in the past year, and it's possibly a very big problem for Meta. Apple in their early days infamously asked candidates if they were "virgins". It was not (as Hollywood likes to portray) about their sexual history, but whether they had ever touched or seen IBM's proprietary code. Apple needed to do a clean-room development and implementation of the same thing. They knew IBM would sic the lawyers on them, and they had to prove they did it using nothing but publicly available info.

The article has absolutely no detail on what these trade secrets might be, or if they will be upheld in court, so we can only speculate. But if these really are trade secrets, and Meta poached them, then we could be talking serious damages or even an injunction.

But knowing the courts, this won't actually be decided for years and it won't even matter by then

Judge: And what forms of inducement did he use to hire them away?

Elon: Uh, well your honor, after I fired them all, he offered them stable employment?

Per the article Meta claims no ex-Twitter employees worked on Threads.

Probably, it'd be pretty stupid not to put his ex-Twitter engineers on the Threads projects. But it's entirely legal to have your employees work on something close to what they did at their last job. I'd be very, very surprised if Meta knowingly allowed stolen IP to be incorporated into their new product, Musk needs to provide some evidence to back his claims.