First off nothing wrong with being a forum lurker who reads but doesn't post. Its effectively the norm these days it seems. The fact that you spoke up about such a negative experience is all that really matters here so don't worry about that.
So while its not against the rules to be "Elitest" this particular character does seem to indeed be "Toxic" in the worst sense of the word. Also its worth noting that while the Terms of Service do state your not allowed to call the player out by name screenshots are a loophole in this rule as its a repost of the content you have paid for in some way or another and as such they cannot censor it under the wording within their Terms or else it would become a violation of use rights as the way in which they have worded it does not specifically call out or state the use of screenshot content from their own game used in this very specific fashion which you as a user are entitled to share. If that was a rule no one could ever share a screenshot with a player name. Which as you can see from their official twitter they do infact allow. Not even to mention the plethora of other boards. Generally speaking the only way they could do that is if you had violated a rule. Of which posting a screenshot is not in anyway a violation. If you had listed his actual name in anyway then you would have been. Loop holes work both ways unfortunately. If I'm mistaken I'm sure an Orange Name Tag will correct this and quote the proper section of the Terms that coincides with that topic matter. They are pretty good at that around here from what I have seen.
As for personal opinion on this player if you asked him to stop messaging you and he continued beyond 1 message after which you did not respond with anything other than "Stop sending me messages please" or something to that effect then you can report them for harassment and would encourage you to do so because that is absolutely incredible that your saying he threatened to get you mass reported. You can report him for abuse of the report system as well in that specific instance. Though I doubt they will act on the second report since reports on discord do not in anyway relate to PSO2 and as such it would be to expensive for them to bother going outside their own platform which is a shame since that guy sounds like a major scumbag.
If you are looking for people to group with without having to deal with people like that there are plenty of clans and player groups both in-game and on discord that are very welcoming. I have my own little merry band of misfits who enjoy PSO2 for instance. Just drop a line to one such group and find some people you can play with so you don't have to risk PUGs with a bad attitude like that guy. If you'd like to get in touch with me to join our group just pop into Our Discord and say hello. Reply here first though so we know who is who since we keep fresh joins locked to filter out players like the one you encountered.
TLDR: So while its not against the rules to be "Elitest" this particular character does seem to indeed be "Toxic" in the worst sense of the word.
Heres a comforting thought... If this guy has a guild that's willing to mass report for him then why is he playing alone taking PUG players ? He is probably just blowing steam and has no one to group with because of his attitude. Take some solace in that.