I think he said what he said to make people talk and make people uncomfortable and it has. The whole situation is uncomfortable, governments sitting watching Israel starve civillians is uncomfortable, seeing children blown to pieces is uncomfortable, seeing governments deny war crimes we can see with our own eyes is uncomfortable.
I think you will have a hard time proving that using a well known phrase like Death to X is illegal unless you are planning on banning all of the posters etc that say death to the patriarchy too.
Calling his zionist boss(and if he did speak like I remember Bob Vylan saying then he clearly was a zionist) who obviously made him extremely uncomfortable a 'fucking zionist' isn't illegal. Context is important here, was his boss Jewish but not zionist? I don't know he didn't name his boss, didn't speak of his ethnicity, I don't even know which boss he was talking about.
LHe will have said these things knowing that he was risking his career and he decided it was worth it so clearly this topic means a lot to him.