Hmm, i doubt that because on the info is said the brother was 29 and MC is 26. And on the graduation day he had (I think) a little sister not brother. But I totally agree that there is something the author is hinting at.
The author made a mistake it the age, it was supposed to be 27. They said it will be adjusted later on
Whaaattt that’s crazy!!!! Then I 100% think you’re right. It was so obvious the way he talked about his first love then the scene switching and everybody talking about the brother.
I just know the brother is his old classmate, too obvious to ignore bruh