Earlier this month, it was reported that the couple got into a scuffle with another audience member at the Sydney Opera House in January. Cops were reportedly called after a man "swatted" Kidman with his program, though no further action was taken.
"We didn't know we weren't supposed to stand in the opera. Having not been to the opera before, ever, in my life, I am sensitive to the etiquette," he told the hosts.
As they were both enjoying the "bloody great performance," Urban noticed that a few people around them were giving standing ovations, so they followed suit.
"I stood up and this guy behind me just whacked not me, Nic, just really hit her ... with the program," he said. Noting the guy was an older gentlemen, Urban said he found himself "in a bit of a pickle" in regards to how to react.
"You're a husband you want to protect your wife. Took a lot of restraint -- I was pretty upset," he said. "I think I just looked at him. I said, 'It's a standing ovation!' I didn't know I'm not allowed to."
He went on to add that he understands "there's a tradition" of things you can and can't do and he respects that. But, at the same time, "I was also going by a lot of other people who were standing and having not been there, I didn't know."
When the hosts noted you just don't hit a woman, period, Urban added, "That's what I was most pissed at, don't hit her."
While Urban and Kidman have a home in Nashville, they went back to Australia with their kids since July as Nicole filmed "9 Perfect Strangers." After Keith wraps "The Voice Australia," they'll be headed to Los Angeles for Kidman to shoot another movie, before "probably coming back" to their home country.