GGL withdrew from an exhibition event in his home town in Spain just a week ago because of a groin problem. By the way he played early on in the match, it looked like he hadn't practiced much lately. Anyway, I really don't think there was anything dodgy in this match.
As you say though, it was an exhibition event which is why you shouldn't read too much into stuff like that.
I think the drift was purely because GGL's form has been pretty rubbish in recent times whilst Donskoy has had a good run in the challengers; he is also Russian and it often pays to back the man playing in front of a home crowd.
At the end of the day I've seen a lot of very suspect matches and this wasn't one of them. GGL was a UE machine at the start of the match with Donskoy just having to put the ball back into play in order for GGL to gift him the point. Once that stopped happening he took complete charge.