I really hate when people says things like: you're wasting my time...

Last night I finished Amdapor Keep for the first time, it was not my first time in the dungeon thoug. So, we killed all 3 bosses whithout a single death and at the end the healer attacked me saying that I must learn the dungeon and that I was wasting their time.

Hello!? Its the second time I entered there I knew the fight but not have so much practise on it. How are we supposed to know the fight if it is not doing it?