Rubbing one out is not a fireable offense.
Getting caught tugging on a Zoom call is not a fireable offense.
Using company time and possibly IT assets (laptop) to rub one out (and probably visiting XXX webpages) is a fireable offense. And this is probably the only grounds any organization would have to stand on.
I'm sure company handbooks will get more detailed around the "Do's" and "Don'ts" of a person's conduct on video calls.
We've all seen the videos of people accidently putting themselves on video when using the bathroom, changing clothes, picking their nose, etc. Additionally with Zoom, the meeting creator can "End Meeting for All" once completed and it auto kicks everyone off the call. I've seen many times where people remain on video and have no idea because the creator did not "End Meeting for All."
I personally do not think CNN had enough ammo to fire him without major legal ramifications from Toobin's party.