It's a bit ambiguous, but my personal reading is that if we assume Abeken is right about the nature of the personal death ghost thing, that the PoV character punching it caused reality to align such that Abeken got punched.
This is the real mystery, yes. Because if they rode the Ferris wheel together, they must be going out? But she's talking to another guy? And Abeken even says they aren't going out? It just makes no sense.
Re-read it after thinking of all your comments... and what if he got punched by Hoshino because he lied about riding the ferris wheel with Inamori... getting caught lying that you're dating someone you're not is quite the horror story
It's a bit ambiguous, but my personal reading is that if we assume Abeken is right about the nature of the personal death ghost thing, that the PoV character punching it caused reality to align such that Abeken got punched.