What? Phone numbers are great! She can even text him if she wants!

Ryoji recognizes that technique, because it's one he kind of uses himself. Though he's not sure which of them use it more intentionally. "Well, I guess because even if you can totally take care of yourself, I get worried when people your age are wandering around alone. And it's always nice to make new friends, isn't it?" The first is far more the motive, but depending on her perspective the second might be more appealing. Or believable.