Am I Psychic or Am I Just Always Right?

Another night of heroics for me yesterday. With a bag-full of balls-ups to go with it.

I was tanking in healing gear, players were lying dead, people were casting aggro generating abilities on everyone but the tank. Still, it was alot of fun. Because it was all with the Munquis.
Wasn't very good for my EPH though (Emblems per Hour).

The first run was the daily. Nexus.
Myself, Bronze, Barry and Lis brought along a new guildy (who I won't name here). From the very start of the run I had a bad feeling about him. (I don't know if it was a he or a she, but it was a male toon).
He wasn't doing anything particularly wrong, apart from the jumping up and down, all the time, thing that the PvP kiddies seem to do (That really irritates me). I just found myself thinking less and less of him as the fights went on.

He was polite enough, and ready when he needed to be ready. But he seemed to be a little irritating. No sooner had I mentioned my dislike in Officer Chat than things began to get a little worse.
He started spamming the DPS meters in Party, and in Guild. And he cast Army of the Dead the very second the Keristraza activated, meaning that Bronze had to mash his buttons to try and keep aggro in his direction. After we all survived the fight... luckily.
Myself and Bronze pointed out his error with Army of the Dead and explained about the Dragon Boss NoseCone damage. The new guy apologised, again politely.

And then 5 minutes later he left the guild.

Now me and Bronze weren't particularly hard on him. And anything I said about my concerns was in officer chat only. So why did he leave?

Because I was right all along. There was something Not-Munqui about the guy. Maybe he was just a little immature, maybe he bought his account on eBay, or maybe I'm just Psychic.
Either way, he'd be welcome back into the Tribe, because he didn't do anything 'wrong', and he even said goodbye before he /GQuit, so maybe we'll all see him again.

Do you think we were too harsh on him? Maybe us older and wiser players expect too much of newbies. We all know the rules about dragons facing away from the group, and that it's not socially acceptable to spam DPS meters between every trash fight. But how would a newbie know?