While the word aliens was foreign to him, the explanation helps. "I've never heard of anything like that...I'm sorry for your losses." While there had been invading prides at times, the hyenas attacking the pridelands, it wasn't such mindless violence. Most disputes were for food or land, and they didn't end in mindless killings. Nothing went to waste on the pridelands.

Though at his last question, Simba smiles, nodding, "I am if I'm needed to be."