I'm not sure what to say to this.
I agree it was inconsiderate of him to agree with you to make it a small, private server for you and your closest friends only for him to invite about 20 people to join you in the server.
If he was going to turn around and do something like that he should have talked to you about it first.
I don't think you should have insulted his gaming friends like that, though.
Have you met these 20 friends yet, or did you just insult them without talking to any of them yet?
He was right to defend his friends like that. If you're going to insult his friends like that than it is perfectly okay if he doesn't want to hang out with you anymore.
So, yeah. My advice: Don't insult anyone's friends.
But I would have been annoyed as well if it happened to me.
Your question about why N.T's have so many fake friends?
A lot of N.T's have a high number of friendships. Like, really fr*cken high.
Even 'shy, awkward' N.T's still manage to have their own little 20+ group of friends...
Don't worry about Quantity, just quality.
Make good friends who treat you well and treat them well back.