Shortly after halftime, the Toffees man appeared to dangle a leg out in the penalty box with Red Devils striker Anthony Martial going over the outstretched leg. Initially, referee John Brooks signalled for a free kick in Everton's favour as he booked a bemused Martial for simulation.
Inevitably, the decision was then sent to Stockley Park, with VAR deciding to overturn the on-field decision and Brooks to the monitor. Speaking on Sky Sports' Ref Watch, Gallagher said: "I thought it was a penalty when I first saw it. It is difficult to say it is not a foul, he dangles his leg and does not get the ball, his leg is planted as well. When you see that, I just do not think there is anything else you can give but a penalty.
"I think Martial is quite happy to go after the ball, but the leg is planted. If you dangle at leg like that, you run the risk."
Once the decision had been made, opening goalscorer Alejandro Garnacho appeared to lead protestations that if the incident was a foul, Young should be booked. The defender had already been shown a yellow card in the match and a second booking would have been a red.
Gallagher reasoned: "The referee obviously thought it was careless. It possibly is a second yellow card, but I would not say it is guaranteed and the one thing I would say is to go from a dive for one player to a red card to another is quite a spectrum to travel. I just wonder, has the referee made that much of an error?"
Marcus Rashford went on to score from the spot and make it 2-0, before Erik ten Hag's side went on to bag a third through Martial and put the game to bed. Speaking after the match, Everton boss Sean Dyche said: "It's bizarre, we all know what's going to happen.
"The screen thing is a farce. Everyone is talking about speeding up the game but when they come to the screen we all know what the outcome is going to be. Good or bad decisions, call it and get on with it. Why do they stand there staring? I haven't seen a referee overturn one yet. He stands there listening then gives exactly what he has been told. I feel for fans. VAR this year has been all over the place. It's the simplest thing but it seems to be mayhem all the time."