Why would anyone be happier on a 26-hour schedule if they can get an adequate amount of sleep and go to sleep close to the same time on 24-hour schedule?

I can see it going the other way, where if your natural rhythm is 22 hours you can likely force yourself to stay awake to align with 24 (and likely would be much happier than free-running on a 22-hour clock).

Speaking from personal experience, if I could consistently stick to a 24-hour schedule, I would. And I think most people with non-24 have the same position (and have likely tried many things before giving up, as tossing and turning for hours every night and then still not sleeping enough is pretty unpleasant).

Additionally, if Bob's rhythm is 26 hours then his sleep cycle is shifting ahead by 2 hours every night regardless of when he falls asleep. If he is able to fall asleep at the same time every night, his sleep cycle presumably isn't shifting, and even if 26 hours might be more natural for him, he's able to sync his cycle to 24 hours regardless.

So I don't think this would qualify them for non-24, as the circadian rhythm isn't shifting every day.

On the other hand, if Bob chooses to sleep 26 hours for whatever reason, perhaps he could be said to have it then? It's just inconceivable to me that someone would actually choose that given the option.

It's worth noting that the average human circadian rhythm is closer to 24.5 hours when external stimuli are removed. So it doesn't strike me as too different from Bob; people are nevertheless regulated to 24 hours by daylight and not said to be non-24, even if, like Bob, their natural state might be to sleep more.