The United captain opened the scoring after a well taken freekick which beat goalkeeper David Raya, left Arsenal supporters frustrated when it was later revealed that the defensive wall was set 11.2 yards away from Fernandes by Taylor rather than the regular 10 yards.
This was highlighted on Sky Sports, Gallagher says Taylor may have factored in that players tend to try to take a few paces forward and that he had followed guidelines.
"The referee felt it was ten yards and in fairness to him, the law says minimum of ten yards. It doesn't say they can't go back 11," Gallagher said on Sky Sports.
"He may have factored in that when a free kick is taken, the wall moves forward anyhow so by the time the free kick is taken, it's closer to ten. I'm not sure the calibration (of the measurement) is right anyhow, but Anthony Taylor will have his system of measuring ten yards.
"The pitch is cut in six yard sections and looking at the pictures, it doesn't look to be much of ten yards when you see it.
"There are guides for referees to help them."
United midfielder Christian Eriksen admitted that the distance was noticeable and may have played to their advantage as they took the lead at Old Trafford.
"Very good, happy that the wall was about 15 meters away. You saw how far back they were and it was beneficial for us.
"We felt relief from the fans in the stadium after the goal."
After dropping points once again, the Gunners remain second in the Premier League but are now 15 points behind Liverpool in a title race that could end well before the season finishes if manager Mikel Arteta cannot become more consistent with his results.