I have no proof. The only thing I noticed is that his POW nonce is different from everyone else.

I've explained the likely reason for that in the #mining channel on steemit.chat.

From what I've seen, my only conclusion is that he is most likely not using an exploit, but rather using his own more efficient custom implementation of the miner. If we take his account name at face value, it likely means that he has built a GPU miner.