He doesn't ask how she can do that...that's not for him to really ponder. Despite the fact she's a detective, he trusts her words, before bringing a hand towards his mouth to let out a whistle that could be easily heard from Kanji's earshot.

"See you later."

With a nod at her, he'll jump away and off on a rooftop, waiting to make sure that Kanji was going towards her before leaving entirely.