Just because a way of expressing is not the absolute rudest thing you could think of doesn't make it a euphemism. If anything, under normal circumstances, "Do this or be fired" is a dysphemism for just telling somebody to do something.

I mean, we're talking about a situation where clearly people hadn't been doing something they'd already been told to do, and somehow expected not to be fired over it.

It's actually not clear that they'd been told to do it (at least, not clearly) based on Ben's description of the situation. Nowhere does he say anything like "I'd talked to this guy about this before" — instead, he talks about how he leads by example and throws out lots of suggestions that he doesn't really expect to be followed.