I don't agree with that assessment, but I do wonder why mention the client or client non-payment at all. If he wants to bother to mention the breach of contract, he should go all in and publish the client's name. Otherwise, just publish it as code written on his own time. (Which it was, at the end.)
If I were to hire you, can I trust that you would not publicly complain about a disagreement? This needs to be asked because this simple act, even though your anger is justified, calls into question your ability to act professionally.
I would recommend removing or rewording the complaint about the client.
Never, never, never publicly complain about a client in a way that can be linked back to you and/or your client.
