I multibox myself and there is nothing wrong with that with the TOS (and you can register up to 8 game accounts per SE account). Since i'm not a human octupus, it's clearly not as good as human controlled char and you heavily using follow and have hard time for micro management. So yeah, that could be kinda weird and you can be really bad in a learning phase of a dungeon. I think he was not able able to complete it with is 4man group, so his tank or heal leave for the final boss to have less things to do. I don't think it's nice to do on a duty and i usually ask friends for that if i need so, but i don't think that's something a bot will do.
That's say, it could be a bot user who just level up his bot using something that's look like legit boxing (or level multiple chars with boxing and plan to use them to bot after), their is no magic way to be sure. Best bet is to usually to ask. If he use joke in name, my bet is it's legit. Some hint could help to see the difference, if he reply, if he's doing his epic quest, multiple jobs, tribal reputation, own a house ...