Technically speaking, yes. By pleading self-defense you're making a justification defense which means you're effectively saying that you did kill the person but you were justified in doing so.
But please, by all means, go on with whatever point you plan on making instead of beating around the bush.
Technically no, especially when you are acquitted of all charges. He did not murder, he killed in self defense. Who needs words and their definitions though. Murderer sounds much worse!
But regardless all that is pointless, the people who think that Zimmerman started something with Martin all believe Zimmerman is a murderer, and the people who think that Martin attacked Zimmerman all believe that Zimmerman acted in self defense.
Did Zimmerman deserve to get jumped? Probably not. Did Martin deserve to be detained? Absolutely not. Could both have happened? Could neither have happened? With all the evidence the Prosecution presented, you still cannot possibly say you know what happened, which is why he was acquitted.
It is as simple as that. People need to start moving on.