Hmm, interesting. I definitely did not tell him I couldn't perform the work. I told him I was concerned I may be developing symptoms of carpal tunnel, and that I wanted to visit a doctor to check. He specifically asked me not to use worker's compensation. Then later in the day he sent me a text message telling me I no longer had a position and cited the two issues that I mentioned up-thread. According to my understanding of the local laws, it seems like a pretty solid case, though clearly I have my own biases to consider.
In my reading, I have repeatedly come across the notion that the timing of the event is really important to the case. Like, if 6 months pass between the event and the individual getting fired, it's tougher to claim that the specific event provoked the employer to fire the person. Whereas, when it occurs on the same day, you can make the assumption that they influenced one another.
In another life, I would have been a lawyer. This stuff fascinates me.