The only goal of an otherwise unremarkable encounter at the KC Stadium on Saturday came from the penalty spot in the 22nd minute, as Robbie Brady converted from 12 yards.
The spot-kick was given after former Hull defender Michael Turner was adjudged to have fouled Yannick Sagbo – who was sent off five minutes later – and the decision infuriated Hughton.
"I thought it was an incredibly soft penalty," Hughton told reporters.
"If the lad [Sagbo] was just about to head the ball in the back of the net [it would have been acceptable]. but the lad was never going to get to the ball.
"The ball was going over his head. Is there some contact? Yes. There is contact with him but you see that in every game.
"Most of you [journalists] would have seen an incident slightly before that, there was certainly a bigger claim for a penalty. From the corner when Curtis Davies pushes Michael Turner.
"If you look at the two, [if] you are going to have a penalty for Hull, then you have to give a penalty to us."
Hughton was also disappointed with his own side, who failed to make the most of their numerical advantage.
Sagbo was sent off in the 27th minute for an off-the-ball clash with Norwich's Jonny Howson, but the hosts desperately clung onto their lead.
That was despite Norwich's best efforts, as they threw men forward in the latter stages, and Hughton bemoaned their failure to equalise.
"It is a missed opportunity. Apart from the penalty, John [Ruddy] really hasn't had a save to make," he said.
"But we came up against a very resilient Hull team. That can happen sometimes when you are down to 10 men.
"They made it difficult for us but we needed to show more quality in the final third and more quality in our final ball."