im not sure what is supposed to be an adult way of acting even as an adult myself. what I can observe though is (1) he doesn't treat the others as people actually, right now, from the mc's pov, he sees them as characters from a story he read, (2) he is goal focused: to go back home for the lottery that he won so he would do everything for it. (3) he acts as if he is not part of the plot which is connected to point 1. he still treats everything as the story that he read. (4) why is he in denial? because of point 2, the lottery he won was a HUGE sum of money that he refuses to be absorbed to the story.

Everyone's loving these but here I am thinking that the mc is just full blown idiot. Imagine he is an adult but he doesn't act like one