"LeightonMcKee slain by Zombie" when it's a Zombie Pigman

I was playing on a Minecraft Survival L.A.N world with my friend, and we had full diamond, I had enchanted tools and an Enchanted Helmet along with Enchanted Boots. So we made a nether portal and got to the nether, and we went to the nether. And when we went to the nether we found a nether fortress. So naturally, we went in. And I attacked and killed a "Wither Skeleton" and only got bones. But I also got attacked by it, so I had the "Wither" effect. And then after walking around for about 10 seconds, I got killed by a "Zombie Pigman". But it said; "LeightonMcKee slain by Zombie.". So I'm wondering, why doesn't it say; "LeightonMcKee slain by Zombie Pigman."?