From what I can tell of the story, he was never left alone with 1 person at any time. He was ushered from room to room, meeting groups of people the whole time.

Personally, I think the culture sounds great. But if he didn't, there's no point in wasting his whole day there. He was polite in telling them that he didn't think he'd fit and there was no need to waste anyone's time.

Had this been a 2-hour interview, instead of a whole day, I'd say stick it out and be friendly. But not a whole day.