I am sorry that I'm late to this but
she remembered him from his first name even after he changed his last name?
It's in the computer, she look it up in the computer. You can see that she's even confused when she sees someone with the same first name.
took her a minute to find what he owed from 10 years ago?
Yea, It called being organised. From the database
in the computer, she knows about the date mc borrowed, the name of the book, and where to find it.
mc just changes moods from joking to serious and the others go along with it at a moment's notice
It's called moe gap. It is a really old trope by now.
how tf did the buff guy know mc wanna know something from literally ZERO CLUES
It even said in the manga that someone saw him looking over the book.
There is no subtext, no need to even think deep, it's right there in the word, in the picture. Do you even read, or you just skip pages and then complain? Let me guess, when you play video games, you skip all cutscene, then critize the game for being "not making sense".