Maybe he had friends? And there are some things that arent' on that half-second global cooldown, though they aren't spells, they're consumable items (food/water), though maybe arcane torrent's not on the global, I don't recall (I barely use it or even think about it). Anyway, even one priest can cast enough debuffs quickly enough that if you aren't paying attention when he hits you with the first few it can seem like he's hit you with three or four at once.
edit: ya, I've got one "silly" macro and one serious on my mage: the silly one yells "HAAKA PAALE!!!" (which, I've been told, is Finnish, roughly translating as "Cut them down!") and activates Mana Shield, the serious one puts a focus on one enemy and lets me polymorph that one even with a different enemy targeted. I also used to have one that put a big x-shaped pair of "Gratz"s down five lines of guild chat for when someone put out a ding, but that one hasn't been working for some reason.
edit2: my dad subscribes to a Latin (as in the language) e-mail mailing list and he found out recently that there's a new guild on some server that does things only in Latin. I figure that if they're horde on Darrowmere we can grief them for being so highbrow at some point. Just a thought.