An apt description of disturbingly many workplaces. This type of "superior" person can hide themselves quite well and have a decent working relationship with their "inferiors", but when challenged will show their cards.
The difference here was that OP had the power to say no, and wasn't trapped by obligations.
I have the impression that some commenters resent them for having that level of self-determination and make excuses for the behavior of the employer.
When you call out someone trying to lowball you and they start ranting, they're really ranting about a narcissistic injury to their self-image.
Someone who does that will be a terrible client, because they're operating from a position of contempt for the people they employ. They do not see you as an equal, but as an inferior.
If the "inferior" challenges their default entitled one-up world view by expecting to be treated like a competent and well-compensated professional, they're absolutely going to have issues with that.