The reason it's an inaccuracy (not a blunder) is because it violates the opening principle of not moving a piece twice unless it forces your opponent to move twice. He burns a tempo and essentially gives up the advantage as the white player.
On top of that, he gives you a very strong d4 pawn. the e4 pawn is the only other piece that would be able to threaten it but clearly you now control that square as well.
For move 8 white clearly has to move his queen. However, it would be illogical for him to have placed his queen on b3 only to pull it back to c2 the next move. But as far as I can tell every place that the white queen goes on that queen side is a bad location. This means 7.Qb3 was also an inaccuracy.
Essentially, white's move c4?! equalizes the position and Qb3 gives black an advantage.
Personally, I'd go about this position by either playing Na5 to harass the bishop or b6 and start destroying white's pawn chain. b6 seems more like what a gruenfeld player would play (attacking the center pawn chain).
So there ya go.
i've come across this move a few times already (and i'm very new to the gruenfeld defense). there are no games with this move on games explorer (i'm assuming because it's considered very poor), and my engine pretty much considers it a blunder. however, i don't really see anything i can capitalize on right away. my analysis pretty much suggests developing as normal.
i'd love to get some analysis of this line. is it really as bad as my engine and the lack of masters' games suggest?