Ivory Coast international Sagbo had won the penalty that saw Hull score through Robbie Brady - a decision labelled "incredibly soft" by Canaries boss Chris Hughton - but minutes later was sent off after he clashed with Norwich's Russell Martin.
It left Hull to play with 10 men for more than an hour but they held out for a deserved three points.
Bruce said: "The boy was silly - it was a rush of blood. He's done something stupid but we have got away with it today.
"I don't know whether it had anything to do with the penalty. It's one of them when they are both grappling with each and he has put his head there.
"He hasn't headbutted him but he has gone through the action and when you are 10 yards away from the referee you are going to be red-carded and rightly so. It was stupid."
Bruce said the challenge by Michael Turner on Sagbo had been "clumsy" but admitted: "We have seen them given and not given at other times."
He added: "We have done fantastically well to hang on and defend for our life. The sheer will to hang onto the result was evident for everybody to see.
"The goalkeeper has made a couple of saves but they couldn't really create the chance that they wanted which we are delighted about.
"All credit to the players to have the legs and the attitude to get the points."
Hughton admitted he had been hugely frustrated by his side's performance and claimed the turning point had been referee Mike Jones' decision to award the penalty.
He said: "I thought it was an incredibly soft penalty. If you give that then there was an even bigger claim slightly before when Curtis Davies pushes Michael Turner at a corner.
"It was a soft penalty - the lad was never going to get to the ball, it was going over his head. There is some contact but you see that in every game."
Hughton said his team had then failed to take advantage of having the extra man.
He added: "We certainly had enough possession but we came up against a very resilient Hull team and that can happen when they are down to 10 men. We needed to show more quality in final third and with the final ball.
"This league is too unforgiving with too much quality and everyone is fighting - they were down to 10 men and fighting for their lives.
"For us it is a missed opportunity and apart from the penalty our keeper has really not had a save to make."