What narrative is there to control? It's not like Twitter was about to put a big post out saying we fired him. He put all of this out their on his own. He wouldn't even need to bring up being fired in interviews, just say he left
He will be effective in doing so because the email screenshot he included indicates exactly that: he was fired for non-performance related reasons. "Your recent behavior has violated multiple policies" is pretty unambiguous to me.
I think the operant phrase is “policy violations.” I’ve never heard that associated with anything but breaking a corporate rule: talking to the media unauthorized, leaking, harassment, etc.
If I had headcount for his particular role, I'd hire him in a second and let him know it's OK to continue making his cartoons (which are very on-point and useful to execs who want to learn more about their orgs than what their middle managers are telling them) but he should of course be aware that my abilities to protect him if an SVP gets annoyed are going to be limited.