At least one juror cited it as his reasoning. It wasn't fully invoked becasue Zimmerman was being straddled at the time of the shooting, so the law didn't technically have much merit. The defence mentioned it, used it, but didn't genuinely invoke it.
They had to prove Zimmerman didn't start it but they couldn't. They couldn't use syg because starting a fight, then ending it with deadly force, is not grounds for syg.
The defence had to convince the jury that Martin escalated the fight to a lethal level. They did that with the whole bashing head in to sidewalk thing. Syg was central, but not the officially invoked law on defence.
I know pleanty