I dont know how you tell (i suspect he wasnt) but just curious to know...
http://en.lichess.org/tMLzJSmE#0Let me ask the black anonymous player whether he cheated or not, hold on a sec.
Such wit!
Usually if someone scores 0 mistakes etc its a sign of cheating, I know sometimes some folks can play a perfect game now and again, apparently Thiabalt and co can spot a cheater and the difference, I dont know how they do it but apparently they can with a fair degree of certainty, yes probably they go by a few games in the history etc but yeah anyway thanks for your helpful comment!
16....Qa6 is a clear indication of an engine enhanced playing account.
I would disagree. It would depend on the time limits/controls.