You could add anyone as a mod to a sub you moderated, he was added as a joke
Even more context they did give the guy who ran it and most the other nswf subs a special award
Fair point. He could be just an absolute bonehead who for whatever reason wasn't able to process that he needed to get the avowed overt pedophilic activity off his server, and didn't see the problem even with them joking around about how he was on their side and giving them an award. There's no particular reason to think that he himself has any inclination that way.
The comment editing was clearly a joke
This is a perfect example of something that's a joke when you're the one with the power, but if you're the one on the receiving end is absolutely not a joke.
I suspect that if someone at Google (or whatever) was editing spez's emails for any reason "as a joke" then he wouldn't be entertained by it in any capacity or think it was okay, however harmless their edits were according to them.
I wouldn't block the number, to keep gathering evidence if any comes, but I 100% agree with reporting to HR. And the police. Depending on the details, you being in his car and them refusing your explicit request to be free of the situation may have been a crime.
It's unlikely that anything will happen to him, but having a police report on file will (a) be a useful piece of information to have recorded objectively, if in the future he does anything else to you or someone else (b) be a deterrent; it will dramatically increase your safety if he knows that you're okay with involving the law to protect yourself against him.
He'll probably be upset, if it goes anywhere. Fuck him. That's a tactic to put pressure on to discourage you from protecting yourself.