There are certain players in the game who try to exploit areas the match engine doesn't quite simulate correctly. This guy's strategy appears to be left sided attack.

What I generally do if I play someone with an unbalanced formation is to unbalance my formation to counteract it, i.e. against this guy I'd play heavily down my left flank and cancel out his advantage. If you can make your formation not illegal in the process then great.

I would suggest that at higher levels more experienced players would find ways around dodgy formations so players like this wouldn't enjoy the same success.