The "help" button explains it pretty well, I thought - in a sense it's "perpetual" Rock Paper Scissors. Q beats W, W beats E, E beats Q. As you hold down one of those keys, if the other guy is holding down a key that beats you, you start losing (and vice versa).
I really like this concept, quite the fun idea.
I am not certain but I think you mash 3 buttons. The player who presses these buttons the fastest win's
Paper-Scissors-Stone => Q-W-E
There is a help button top-right.
Certainly a viable strategy, although as other commentators have pointed out - it's easily countered by simply holding down only one button and thus forcing opponent to stop mashing and find the correct counter move.