I've met the kind. Be thankful it was pre-50, where idiots aren't going to end up killing you and wiping the group.
The problem could have been any one of a number of things. If he wasn't responding, he might not have been reading chat and simply continued on thinking he was doing what he was supposed to (I've met some people new to MMOs that think they're supposed to use their taunts even as DPS because they think it allows them to deal more damage or something). He could have simply been an idiot that believed that he could be both tank and DPS at the same time in the same spec (because some people don't realize that being able to queue for multiple roles does not mean that you can actually perform both roles simultaneously). He could, just as easily, have been a ******* DPS trying to piss you off for whatever reason or an amazingly competent DPS just trying to ease the load on you.
The important thing to consider is whether or not he responded back to you in chat (or whisper). Generally, if I complain at someone or ask about their spec/abilities they're using (like why an Infiltration Shadow is using Mind Crush or a VG tank is using Full Auto) and they don't respond, I take it as a bad sign. If their behavior is especially annoying/egregious and they refuse to defend themselves, I generally kick them or quit the group. DPS is easy enough to replace and, as a tank, I can find a group again quickly enough. If the guy is being a hardcore baddy and doesn't even have the decency to respond to party chat, I'm not gonna bother continuing a run with him.