Well he does say:
We know that in “Space Seed” they talk about Khan being the best of tyrants, that he ruled with… how do I put this? He wasn’t a cruel ruler. There’s this famous line where in the episode they say he didn’t start wars until he was attacked. So it’s that sort of taking little things and extrapolating, “Well, what does that mean?”, like someone else attacked him first and then the war started?
Basically he's saying that while Khan might think he's a good guy ruling for the greater good, that he's still a meglomaniac and still evil. He's trying to disabuse the whole "the guy's puppy died as a kid and therefore he was traumatized" stuff.