It's not against rules to have few accounts on one PC running at same time to have advantage? No. Ahhh. Ok. Well i still suspect him cheating but nevermind.
Today i met these guys Rexas,Falgern,Traxanz and they all were from same faction and it seemed those 3 accounts were used on same account. Can you check console and see what IP they use to connect? I dont think it was fair.