Ok, that makes more sense. Arcane barrage has a high weapon damage percent scaling, so if the elven spellsinger rolled a very strong weapon it could have the effect you described. Thanks for the clarification!
Spellsingers have a sight range of 10 tiles without infravision, so nothing special. All enemies, just like you described, don't chase after a couple of turns, but they don't return home at all. They wander around or do some specific activities. I think you might have been unlucky so that the spellsinger simply wandered off in the same direction and found you.