Is it possible that you were not at full health' either due to the wipe or because someone cast the endurance buff? If that were the case and the healer was actually healing something and not just using the attack I think that it would pull aggro. At least I feel like I've accidentally pulled that way before xD.
Yeah I was at full health. Now it's apparent his gun heal didn't pull, but he did. He just so happened to be spamming his gun heal on me at the same time. He got to close to the mob is all, plain and simple. However, when mercs just spam the gun heal for no reason when the target is at full health, it is very annoying. At least the commando's version doesn't make noise.