This occurred on the fourth floor of my campus library. For reference, the first floor is classrooms, second floor is a talk friendly study place, third floor is a quiet study place, and fourth floor is the computer lab.

It is my understanding that there is an unspoken rule that unless you are working on a group project and need to talk with others to get your work done, the computer lab is also meant to be a quiet floor.

I had been at my computer for a while doing some required reading when another student walks in playing music on his headphones loud enough that I could hear him from across the room (maybe 50 feet away). He sits down and proceeds to look at his phone, not logging in to the computer and not turning the volume down for maybe 5 minutes. At that point I got up, walked over to him, tapped him on the shoulder, and said “hey man, can you turn your music down? It’s hard for me to focus”. He looks at me without saying anything, and after a moment he turns his music down and I go back to my seat.

Fast forward 30 minutes or so he walks up to me and asks if I worked at the library. I told him I didn’t, and he responded “why did you ask me to turn my music down”. Being socially anxious, I nervously said something along the lines of I’m sorry if I offended you but it was really distracting. He kinda shook his head in disbelief and then walked out of the lab. AITA?

Some more information that I didn’t know where to put in. 
 - There were maybe four other people in the lab at the time including one campus employed student who was there to help with IT problems. Non of them said anything or seemed to notice any of this take place (as in it didn’t distract them).
 - The headphones he was using looked like the old generic apple headphones, which if anyone has used them knows that they become miniature speakers past half volume. His music wasn’t loud, but it was noticeable enough that I could hear the baseline and a bit of the melody.
 - I had headphones visibly on me (phone in pocket, headphones going through the shirt out of the neck) but I was not wearing them because my own music was distracting me from the reading.
 - There are some computers on the second floor, but they can’t be used to access canvas, a site many teachers use to post assignments and grades.