I suspect that doing it this way puts pressure on the core team members who don't subscribe to the behaviors moderate the people on the core team who are problems. But one can never know.
Yes, that's how I read it too. At a guess, if the threat to resign didn't change anything the resignation also won't change anything and strongly suggesting the core team can not be trusted not to lie is a very harsh move that has the power to destabilize the whole Rust experiment. Massively dumb move this.