I'd be more likely to assume that it's a really great one, where folks like and trust each other enough that they can give each other crap like this and everyone understands and appreciates it, like good friends trash-talking each other on the basketball court. I've thought for years that the way you can tell acquaintances have become friends is if they start insulting each other.
Or, as you say, it could be a really horrible environment - but I don't think you can tell from one anecdote.
Considering how many people love telling this story, both within and outside of Costco, I think it's more the former than the latter. One way you can tell is that the COO, who was cursed at in this story, later succeeded Sinegal as the CEO and, in fact, has gone on record defending that hot dog price many times.