lets say he eventually gets 6 alts to lvl 70, it takes the same amount of XP total to do so each time. So the bot means he spends less of his time getting to level 70, but overall makes the exact same amount of XP, he will either in person, or VIA bot spend an almost identical amount of time "camping spawns" for XP, and once you hit lvl 70 it becomes a bit pointless to camp spawns of things. So at the end of the day, because theres a finite limit on what you'll end up getting.
So either you'll see him and his bot for 3 months , or you'll see him and no bot for 6 months, it really won't make much difference in the grand scheme of things.
So a guy was there before and after you logged in, I've seen that in many MMO's without people using bots. There are thousands, millions infact, of people in the damn game, if a bot isn't on a spawn, a real person would be.
Infact i never used a bot, don't think i came across one, but the amount of times i needed a named mob, or a specific type of kill and other people were killing them and "getting in the way" was insane. I would have probably happily used a bot to avoid the wait and monotony that came with waiting for rare mobs/spawns with huge groups. Leave a bot there waiting for it and kill it while i'm doing other things, so i don't sit for 3 hours in game being beaten to the kill by some random stealthed guy i couldn't see, or a faster induction attack from someone else.