If he had competing offers, he was in a good negotiating position. I can understand believing in a great company and drinking the kool-aid, but if you have competing offers and a company explicitly states, "Salary and equity are non-negotiable" - that's a huge red flag.

You should be allowed to negotiate as a savvy prospective employee. With very few exceptions, you don't want to put yourself in an environment where terms are dictated to you rather than opened on a floor with you for your input. Even if you fail miserably at the negotiation, at least you had an opportunity.

Second to this - unless you're literally at-will employee, this is grounds for liability. The author was explicitly told, "You didn't do anything wrong, we're just getting rid of you because you don't fit." IANAL, so I won't harp on this as I don't know the particulars, but I'm fairly sure this is a case most lawyers wouldn't shy away from if everything is to be taken at face-value here (anyone with a law degree can correct me if I'm wrong).

In any case...I'm glad the author received validation of his abilities, even if it was nearly a year later. Maybe his former boss will grow a backbone and rehire him for something awesome. At least he didn't burn a bridge.