While I agree with most of what you said, I think that the idea that this is a result of carelessness mixed with callousness is wrong. Don't forget these are the people that believe in things like eye for an eye, teaching "lessons", divine punishment, and that God provides you with what you deserve. They also know that the Houthis are a tight-knit culture. That they are going to live amongst family and other Houthis.
I have no doubt that the civilian casualties were a feature and not a bug. They chose their targets for the greatest "impact". They intended to send a "signal" and teach a "lesson". And the dead civilians were that message.