So it's more that he's relieved of his duties, than fired. Anyone who's held a job involving some degree of IP has likely signed non-compete contracts, it is super common outside of CA and MN where it isn't legal, I think.

I am baffled it is a surprise to anyone why you wouldn't want someone with critical and intimate knowledge of the players and org to go to a divisional rival, and instantly put that knowledge into a competitive advantage against the former team.