Since he’s been all over the news for a couple years, it would be pretty tough for somebody to claim they came up with the idea without knowledge of his work.
***Basically, Defkalion appears to have done exactly that. They worked with Rossi for a while, had a falling out, then miraculously had a breakthrough of their own which seems exactly like Rossi’s. Rossi is a mercurial personality, so it is easy to imagine that he pushed them to the edge & pissed them off to the point they would steal his IP.
Claims are one thing. Proving it in court is quite another.
If this thing were to work out, presumably it would be worth hundreds of billions of dollars. I think Rossi would be able to afford an attorney.