You are missing something. When I looked this up in my copy of The Amateur's Mind, the sequence mentioned is
6. ... d5 7. Nc3 Nf6 8. cxd5 Nxd5 ...
I'm not sure if you're just skipping past those moves while reading (I know I do that sometimes) or if your copy has a misprint, but you're missing a whole move there.
That's funny, the move is not mentioned in my book. I doubt however, that it is just a misprint, otherwise the numbers of the moves would be different. Do you have the second edition as well?
Anyway, that has already helped me. I will just copy the move into the book. Thanks for the quick help! 
Wait a second - then the ninth move in my edition 9. Nc3 does not make any sense. Is that move mentioned in your book? Maybe the move order is somehow messed up.
My copy says it is the "2nd edition/expanded" version.
Here is the exact wording in my copy:
1600: "I like 6. Bc4. It attacks f7, threatens Ng5 and allows me to castle. He could push to d5 but then I play Bb3 followed by Nc3 when it's equal. Another interesting move is 6. c4 when 6... d5 7. Nc3 Nf6 8. cxd5 Nxd5 9. Bc4 Be6 10. 0-0 is promising"
Looks like omnipaul answered it...error in first Ed. I wrote the moves in
Okay, thanks again omnipaul. That makes sense now. It is interesting to note however, that my copy also say "2nd edition/expanded" on its cover. So there seem to be different versions of that edition.Well, who cares, I corrected it and it should be understandable now.
I have the same 2nd edition expanded and the c4 push was bothering me too, with silman replying to it and not acknowledging the knight still on e4
On page 87 of his great book "The Amateur's Mind" (2. edition) Silman goes over a master game between Fischer and Gheorghiu with one of his student. The moves are
1. e4 e5
2. Nf3 Nf6
3. Nxe5 d6
4. Nf3 Nxe4
5. d4 Be7
I checked them, these are indeed the moves played in that game. However, the student proposes 6. c4 along with the follow-up 6. ... d5 7. cxd5 Nxd5 8. Bc4 Be6 9. Nc3. Which knight of black's is supposed to take on d5? The only piece that can take on d5 is black's queen, but than the next move 8. Bc4 would not make sense. Later on he even repeats that seqence and comments on it's value (not mentioning of course that it is impossible anyway). Am I missing something or should I just ignore that passage?