If you know of and share a world with one of his alts it makes me think there's more to this than just you asking someone to heal in a dungeon, seems like we may not be getting the whole story and that's why this person isn't banned.

Calling someone names in game is wrong and if he called you an idiot for literally just typing 'heal pls' then it sounds like he does deserve more punishment than he recieved but I'm skeptical of the whole situation. To just know of an alt of a random pug and pick them out in shout chat seems really odd.