No irony in this story because United simply only permits dogs and cats in the cabin, not other animals. The problem in this case was the uninformed gate agents in Bozeman who should never have permitted the family to board in the first place. And, United has recently updated its policy regarding emotional support/comfort animals as well.
On a lighter note, I know a woman on the East Coast who raises Cuys and who related a story of carrying one onboard out of Palm Springs. When she went through the security check, she opened the carrier just enough to permit a peek inside, and told the security personnel that it was a cat. lol Certainly gave me ideas, but then I wouldn't want to risk getting stranded at the last minute.