My take on this what they were testing whether I could be pushed around, and I won't be. I'd not want to work at a place that plays those kind of mind-games.

You are, of course, correct. You still could have made $XXX/hr for the privilege to continue this charade and then reject their offer.

For someone skilled at doing ML, your hourly contract rate is about 60% too low.

There you go, the correction is made. :-)