Hmm. Others have pretty much said it. Probably not avoiding AoEs or standing in front of mobs, possibly your damage was low. But no matter what it was, it's ridiculous for them to rage when you're only level 23 or thereabouts.

The dungeons at that level are really easy to heal even with a lot of mistakes (they're meant to give a lot of leeway for people to learn). There's not really anything in them that's a serious threat... so yeah, that healer was a jerk.

If you want to go the extra mile for improvement... have a friend come with you and see if they notice anything.