I think it's because it seemed so easy for winz to kill Vo0 on that map (i.e. it was very one sided). Well Vo0 started gathering some frags after that comment (maybe it was a tactical move ;)). And it was Vo0 who first said 'gg' afair (must have been frustrated).
meh, it seemed a little whiny, but it was just friendly banter really -- not exactly meant to be a public statement. I mean, in the context of "why you lie ;[" (the ;[ added in by me to show mood), it's just friendly chat.
I thought that means like "I give up, you have won" even though Vo0 would manage to win by frags later in this map because winz stop playing serious. It's more a matter of honor.
Or can Vo0 still win after saying gg?
Would be interesting if someone says gg with score 1:9 and than manages to win 10:9 ;-)