Gunn, who felt the opening goal should not have stood, said: "Before the game the referee said he would make the right major decisions but he failed to award a free-kick for an infringement against my goalkeeper, David Marshall.
"99.9% of the time the referee would have awarded a free-kick and not allowed a goal. Marshall came in with blood on his nose so there had been contact and I thought the referee was poor and it was a bad decision."
Birmingham manager Alex McLeish disagreed with his former Aberdeen team-mate.
He said: "It was a clean jump by Cameron Jerome.
Marshall should have punched instead of trying to catch the ball.
"There was no contact with Jerome and Marshall hurt himself falling down."
Gunn could at least be pleased with the result.
He added: "I was delighted with the performance of the team but disappointed we did not get the three points.
"We now have confidence in the team and in recent weeks we have shown that we are a good team. It was a fine opportunity for the players to play against such an experienced team as Birmingham and they did themselves proud.
"We are particularly indebted to the loan players such as Alan Lee. He could have joined other clubs but was very happy to join Norwich.
"I was also pleased with the commitment of Simon Lappin on his first appearance after 16 months out of the team. He is a model professional and an example to the rest of the team."
Unsurprisingly McLeish was not so pleased with the outcome.
"We started too casually and the players forgot what I had told them for recent home games," he said.
"We had a good opportunity to shut the game out but then shot ourselves in the foot giving away a free-kick on the edge
of the penalty area.
"We have given away far too many free-kicks away on the edge of the area in recent games and somewhere along the line you are going to get punished, as we were on this occasion.
"Lee Carsley is gutted as he didn't deal with it and clear the situation."
McLeish also has obvious attacking problems. Birmingham have now only scored six times in their last eight games
but they remain in second place behind Wolves, albeit five points behind.
Norwich desperately tried to knock Birmingham out of their stride with some snappy attacks on the break with Alan Gow and Dave Mooney often a threat.
Birmingham's attacking ideas were seemingly very limited and it was over half an hour before they managed to test goalkeeper Marshall when he easily saved a Hameur Bouazza header.
But Marshall was seriously at fault in the 38th minute when he failed to gather a left-wing cross from Bouazza and Jerome pounced to score.
Norwich levelled eight minutes into the second half when Clingan scored direct from a free-kick after Carsley had fouled Lee.
Marshall made amends for his earlier mistake in spectacular style with a last-minute save when he flicked a Kevin Phillips header over the