Eh, he only has 13 disputes after 1700 games. Not saying it's impossible but...
I think an actual cheater would have better than <.50 winrate. You might have just gotten really unlucky.
His profile is Private - check
I got deconnected right when I was about to win - check
I got reconnected the moment I pressed quit game after the Defeat screen - check
How unlucky can one guy be?