Not necessarily.
If the rear of the gun's slide bumped into Zimmerman's body, that would have also interfered with the gun's cycling. If Zimmerman's on the ground trying to fire at an attacker on top of him, it's quite possible that some part of him got in the way of the slide's cycling.
Either way, the lack of cycling is indicative of Zimmerman being in a struggle, and would point towards self-defense by Zimmerman.
True. I was more or less trying to answer the question of why GZ didn’t shoot twice.
I’m pretty sure the “gun jammed” story got started when it became known only one shot was fired, one empty brass was found, and Z’s gun was turned over to police officer with an empty chamber and full magazine. If that is all true, that does not indicate that the gun “jammed”.