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”.
If the chamber is empty and the clip is full doesn’t it mean that gun didn’t cycle. Hence, jam.
If there was an empty chamber, an ejected shell, and a non-empty magazine, that indicates that either Zimmerman took out the chambered round before handing over the pistol (good firearms practice), or that the gun’s slide went back far enough to extract and eject the spent shell, but not far enough to catch and chamber the next round from the magazine.