In the Pirc, bringing a dragon pawn structure fails [FEN ""]

1. d4 d6 2. e4 g6 3. Nc3 Nf6 4. Nf3 c5 5. dxc5 Qa5 6. cxd6


Above you can see the first moves of a Pirc Defense game. To study this opening, I learn with the book "Pirc Alert!" by Lev Alburt and Alex Chernin.

After 4. Nf3, there is a trick which consists of ...c5, ...Qa5 (two pawns are threatened) and ...Qxc5, winning the pawn, ...c5 and bringing a Sicilian Dragon pawn structure, which is very good. But today I played an Internet game (seen above) and White's move 6. cxd6 seems very good. The authors of my book didn't speak about this move.

I had over viewed the position after 6. dxc6 and neither I nor my chess engine. could find any strong reply.

Is the move 6... exd6 strong? What is Black's best reply to 6. cxd6?
Yeah, seems like black just blundered a pawn with c5.
Probably you just mixed up the variation and you really wanted to play:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 c5  


That is quite a common variation, I looked at 6.dc Qa5 7.Qd4 for white a while back, if I remember correctly. So maybe you should just check your book again, it's unlikely they made such a mistake.