It baffles me that you can advertise something as “unlimited” and then impose arbitrary limits after the fact.

I didn't saw anything on the post that suggests that was the case. They start with a reference to a urgent call for a meeting from cloud flare to discuss specifics on how they were using the hosting provider's service, which sounds a lot like they were caught hiding behind the host doing abusive things,and afterwards they were explicitly pointed out for doing abusing stuff that violated terms of service and jeopardized the hosting service's reputation as a good actor.