Wanderers went ahead through Kevin Davies, but Fernando Torres drew level before Cole's late strike won it for the Reds.
"It's cruel because it happened in the home game," he said.
"Maybe that is the little bit of luck Roy needed, who knows, but it certainly went their way.
"I've not had a chance to look back (at the replay) but I know the players are adamant Cole is offside - he is on the paint as he taps it in.
"It has happened to us many times when we've gone to big stadiums and it happened again to us."