Neither Tsukko nor Hinako know that he's carrying around a particular piece of emotional trauma from middle school (as I mentioned in the 10.1 comments). This has made him unable to believe that Hinako actually likes him, and causes everything pointing the other way to be excessively magnified (such as when Hinako denied to Tsukko that she had asked Asahi to the aquarium and instead thought Asahi had asked her).
In the canon pre-serialization
chapter 2 page 7:
Asahi: "I have developed a one-sided love towards her which was crushed once before, about two years ago."
-- overheard in background --
Tsukko: "He's a guy too. So unless you like him that way you should stop."
Hinako: "Ehhh - But he's so cute
like a younger brother." (bold in original)