This could be a DPS that happen to queue as a healer and not being prepared to actually do any healing at all. I have a commando that I barely do any healing with. If I ever get in a healing role I will be probably in trouble myself.
Notice in the story that he had his AoE heal that he was plopping down from time to time. This is the top-tier ability for healing sages/sorcs. He was just a crappy healer.