If I understand correctly, he ignored you, then he killed you all?
There are some specific ways that might happen. For example he could block with the Meridia's Blessed Armor set and all your attacks other than AOE (I think) would miss for 5 seconds. There are probably some other sets or ultimates that have a similar effect. All of these have long cooldowns, though.
Templar is strong right now, but not so strong that they could both outheal and kill 3 good players at the same time. If, however, you and your 2 team members were beginners at PvP then, yes, that is entirely possible. Your PvE experience, however good, does not carry over to PvP nor does your build.
In a BG you usually get matched with people of your own skill level. Usually. It is possible you were up against an experienced, fully min-maxed PvPer instead. Yes, they would steamroll you. That would have nothing to do with them being a templar. They could not do the same to 2 or 3 of their peers and that goes for any class versus any class.
I'm just in shock from pvp. I went to bg at 3 we hit one plane. He placed his rune. And under the stun, either he doesn’t give a damn about us, or his stamina is over. His very healing healed all our wounds. He came out of his stun and rolled us like pancakes. Pvp respect... He just stood dumbfounded for 3 seconds. We didn't even shoot 1/4 of the life.
What kind of inappropriate self-healing is this? Even the dk and the necromancer don't heal that much.