He arrives at this reasoning because Cherry says she would never drink coke.
Explanation:
Cherry is not a coke lover. She claims that she would never drink this drink, even if she was starving and that was her only option. Ponyboy, like someone who likes coca-cola, finds this statement very bad. This takes away all the charm of Cherry for him and it is at that moment that he concluded that they "weren’t alike."
He's just arrived at this place where he finds a shooting star. He gets off his bike and stands by the handles and leans on them. After that, he's wishing quietly upon this star and glaring at this beautiful scenery.
