Yes, though I think this is complicated by the fact that the clerk was beaten with the bat first. He then managed to seize control of it from the assailant, and when the assailant fled the store, I assume being chased by the clerk, he was struck with the bat repeatedly.
I think most people in a situation where they've been assaulted by a crackhead wielding a bat, if they managed to get control of said bat, would be naturally inclined, due to the nature of the situation, to use this bat on the perpetrator, even if he turned tail after his "plan" went sideways.
This is where there's a clear divide between what many feel is "right" and what is legally "right". The idea that in an armed robbery, the perp can somehow become the victim because their plan was poorly executed and/or they weren't prepared for resistance, seems preposterous. They were the one who made the decision to undertake this criminal exercise in the first place, one would expect that they should bear the brunt of the fallout from that decision. But of course that's not how the law sees it.
I must assume that the clerk, freshly assaulted, had no training, legal or otherwise, on proportional response or how to temper his emotions and maintain self control while under duress. After all, if he was trained as a peace officer, he wouldn't be manning the counter of a convenience store at 1:45AM. I think this should have been factored into the decision making process that resulted in him being charged and held. I certainly hope it is factored into his court case.