Lukaku committed two fouls which could have been deemed as bookable offences, but Graham Scott opted against cautioning the Belgian forward for the first challenge.
Howe has suggested that the forward should have been dismissed, but Gallagher says that the offences came the "wrong way round" for Scott to receive direct criticism.
Gallagher told Sky Sports News: "He shouldn't have been sent off because it's the wrong way round. The only time you can criticise a referee is if he gives a yellow card and then fails to give a second yellow card.
"Because he didn't give the first yellow card, all he has done is affected the play. If he saw the first tackle on Ake like we've seen it on television then he would have given a yellow card. He hasn't seen the angle we've got.
"Lukaku's body shielded him when he went into the tackle and Ake got up so quickly it would have told the referee, the ball was just running out of play."
Lukaku scored the only goal of the game in the North-West as United prevailed by a 1-0 scoreline.