I've seen my fair share of weird things while fishing, but this is something new. I've never heard of a fish playing dead to avoid capture. Honestly, I don't think that would be an effective tactic for any threatening situation a fish could find itself in. Well, here's a video proving me wrong.
I would guess this fish wasn't playing dead, it was just very lethargic. Fish are cold-blooded and don't move or feed much when the water turns cold. The air temperature was probably colder than the water, which could shock the fish, causing it to freeze up.
Then again, maybe it was actually playing dead. The cichlid is known to play dead to lure prey close to it. What's to say this one hasn't been caught before and is using the tactic to escape?