McCullum made headlines in the aftermath of the Lord's test, saying his team no longer wanted to socialise with Australia after the Bairstow incident.
Australia's 43-run win at Lord's has left England needing to pull off a miracle to regain the Ashes, having never come back from 2-0 down in a series in the team's 146-year history.
And McCullum believes the anger over Alex Carey's decision to stump Jonny Bairstow when he wandered out of his crease could spark that.
"I don't know if it's anger, but our unit is galvanised," McCullum said.
"There are times as a coach where you've got to reduce emotion because it's going to bubble over and you can make poor decisions, but there's times when you allow emotion to go because it's going to galvanise the unit.
"That's what I felt this emotion did for the side. I looked around the group and the guys were a little upset.
McCullum also believed the incident would impact the spirit of the series, which had already ignited in the first test at Edgbaston with Ollie Robinson's send-off of Usman Khawaja.
England's antics after Birmingham - including claiming it felt like a win - are known to have raised eyebrows in Australia's camp in the lead up to Lord's.
It also hasn't been lost on some that McCullum twice ran out opponents during his test career who were celebrating milestones, including Sri Lanka's Muthiah Muralidaran.
Reminded of that after the Lord's test, the England coach reasoned that he was younger then and now regrets it.
"Obviously I've made an apology to Murali in my Cowdrey Lecture (in 2016)," the former New Zealand wicketkeeper said.
"When I was a younger man I didn't quite understand the significance of what the spirit of the game means to the game.
"It's what the defining point of the game is compared to others, and it's only with the benefit of time and experience that we're able to learn that and cherish it.
"In time, we'll see, but I get the feeling that it might have an effect on (Australia).
"Technically it was out, I just question that Jonny wasn't looking to try and take a run. He felt as if the umpires had intimated that it was over and the evidence backs that up."
England will wait on the fitness of Ollie Pope's shoulder before deciding if he can play the Headingley test on Thursday.
If he is out, Dan Lawrence will likely be the man to come in after the hosts opted against bring gloveman Ben Foakes into their squad.
