From what I've been able to gather, he left his gun in the car. I would say that was his mistake. They could have attacked him before he got in his car and got his gun. I guess that was the only mistake I would say he made.
I personally always carry chambered. I have no fear that my gun will AD. And there are plenty of situations were you might not be able to rack the slide or have time to do so. There's no way on Earth I could rack the slide on my PM9 without both hands. Something odd though, my brother and my father who are both CWP holders as well, think I'm nuts to carry chambered. Always thought that was strange. I always tell them, I feel the same way about you.
Also I was reading a bit more and found one of the assailants FB pages: