This guy forgot that there are people behind every product and the abstraction is as thin as it gets when it is in fact a smaller company or a startup. There are negative reviews and there are nasty reviews. He was nasty to them and they no longer wanted him as a client. No reason why a company should swallow shit that a person wouldn't. They certainly _can_ do that (no questions asked refunds, customer is always right, etc), but it's an option, not a requirement.
[Edit]
We had paying customers like that - sent pissy emails, no Hello, no signature, just spit and complaints about minutae with personal attacks ("only an idiot would do it that way") and a shitload of entitlement because they paid us money. In all cases they recieved an immediate refund and a goodbye. If they can't make a basic effort to keep things civil, we have no interest in working with them.
The only issue with the case at hand is that they explicitly mention bad an Amazon review, while they actually dropped him because of his general toxic attitude.