Well, it's beyond the density. He said he doesn't want to see her that way. Maybe he really doesn't want to get closer to her? Otherwise it doesn't make much sense. Yeah it's comedy manga but this situation is pretty awkward and different from his uncle's encounters. I mean, she blatantly declares she wants him to see her naked and she's happy about the fact he recognize her as CUTE girl, but he just rejects her. I guess she could confess to him and ask him out and his reaction would be same