One of the interesting things about Han is that he isn't completely transparent. He surprises her just often enough to put Natasha off of her surest footing. It's a good thing for his interests, but a feature that rubs at some still open wounds and raw emotions.

She needs time.

"Don't be so sure about that, in my case." It does reassure her, the breathing room. He doesn't wrongly assume he has her pegged, but nor does he try to pry too deep. There's a probing interest but it's sedate enough that Natasha doesn't feel threatened.

"As charming as all of this is, I need to get back to my place pretty soon here. Think you'll manage to not starve and learn about the phone on your own until later?" There will be a later, Han. you've earned that reassurance, at least.