Why isn't this part of the book sequence?

I played 7... c6, which apparently is not a book move. But afterwards 8. h3 b5 is played, which register as book moves. Which shouldn't be possible because that means c6 would also have to be part of the book sequence. Is there any explanation for this?

i don't understand... do you mean that it says h3 is a book move, but d6 isn't?

Sometimes the computer has quite an opinion on opening moves.

It reaches a position that was reachable from other book moves, just not that one.

Transpositions