how was this a missed win?
move 7 is the missed win.
Remember that a missed win is just simply missing out on an advantage in evaluations of the positions, even if there is no obvious win in sight. In most cases, this does not equate to missed checkmate.
7.bb2 kxd5 8. exd5 kb4
white has to defend c2 from a knight fork allowing black to win the pawn on d5