I'm inclined to err on the side of the dog: if she knows the rules, and suddenly starts breaking them, I have her checked. There are other things that can cause UTI-type problems that your vet can check at the same time. The last dog I took in for a UTI (puddle in her crate, drinking/peeing more than usual) had some crystals in her urine, although not enough to panic about.
The first instance sounds behavioural. He got distracted, and you and your DH didn't pick up on his later signal. I suppose one could argue that he was under stress the second time, but you don't seem to think it was that severe. But not being able to stop (when he has in the past), and peeing more than usual are suspicious.
A couple of other thoughts: has he been going more than usual every time, or just sometimes? With the cold and snow we've had lately, some of my girls have been having trouble standing still long enough. I have to watch them to make sure they go long or often enough. (Fortunately, they haven't opted to go inside.) Or does he eat snow? Minnie is a snow eater, and Edie gets some when cleaning up under the birdfeeder. Snow is supposed to be dehydrating, but it sure makes my girls fill up. Have you changed any of his food or treats? Or are you home more so his schedule is off? Perhaps he's drinking more and you're not seeing it?
I hope that whatever it is can be diagnosed and resolved quickly.