fault?

Game id= 1596499

15b- f5 (i moved from F7 to F5)
16w- exf6 (He moved from E5 to F6 and took my pawn)- how he did this?

This is an "en passant" capture. For details:

http://www.redhotpawn.com/help/index.php?help=enpassant

The sticky thread is not helping much, I think...