"If I have to keep information secret, won't you explain more? I can't hide what isn't known to me."

He says, matter-of-fact, and it's not untrue but there's more to it. Kaworu wants to understand Midoriya and why he's so afraid, so concerned. What out there is hunting him? He knows Midoriya is powerful so this must be something of even greater power. A true threat, possibly from the place Midoriya comes from.