The Australian international fired in his 10th goal of the season in 13 appearances after Jamie McCart was adjudged to have illegally blocked the winger’s shot with his arm.
St Johnstone boss Callum Davidson thought the decision from referee John Beaton was harsh on his player and he was backed up by the experienced ex-official.
Gallagher told Sky Sports News: “I don’t know what he [McCart] is meant to do. It’s so close to him and comes so fast.
“His arm is tucked in beside his body and I really felt for him.”
Davidson made his dissatisfaction known after the match as Hibs ended a five-game winless run against the Perth side and picked up their first victory over them at Easter Road since August 2012.
He said: “I didn’t think Jamie’s hands were in a position where he was making himself bigger. I think the ball basically came off his chest area. The guy was a yard away from him. So realistically, I’m not quite sure.
"I think it’s really hard for the referees sometimes. For me, they’ve just got to be sure it’s a penalty. It would be different if Jamie’s hands were up high or trying to block the ball.
‘”As a defender, and I’m sure Jack will say the same, I’d be disappointed to lose a penalty like that. I think it’s just very unfortunate how it’s affected the game."