Classroom Confusion - 5317 or 5137?

I could still remember my first day of class in UCLA Extension. It was a Monday, September 25. Even though my class was at 6:30PM, I came to school at 4:00PM to "familiarize" myself with the large campus of UCLA. I ended up tiring my legs and feet from walking aimlessly around the campus, and my eyes, afterwards, from reading a book on international terrorism, when my lower limbs momentarily surrendered.

At 6:00PM, I decided to start walking towards my classroom. Unlike how I may have looked a couple of hours before, I didn't want to look like it was my first time in UCLA as I was going to my Information Security class. I took out my enrollment receipt and memorized the building name and room number. I planned to go directly to my classroom, in all confidence, like it was just this time of the year when I have to start the term as usual.

Alas, the room numbers for the Math Sciences Building, where my first class was, baffled me. The room number for Information Security started with 5 so I thought my class would be on the fifth floor. It turned out that the rooms on ground level all started with 5 (like 5117 or 5126). Weird. And for some reason, the rooms apparently are not arranged in ascending or descending order of room numbers. Weird again. Now, at the building entrance, there was a couple of people who assisted the new students who were confused with the room numbers by giving the directions to their proper rooms. I had no choice but to admit my newbie-ness and approached one of the guides.

Man: Where is your class?

Rom: It's 5317 of this building.

Man: What?

Rom: 5317.

Man (looking at a list): ... uh....

Rom: Wait, I'll just take out my enrollment receipt (and show it to you since you don't seem to believe me). There. Oh! it's 5137. I'm sorry.

Man: Ah. there you go. It's on the other side of the building. Go past those glass doors. Somewhere on the left side.

So I went ahead. I chose a spot in the middle of the second or third row, I can't remember which row exactly. Time check - 6:20, still early. I went out to find the restroom, which I was told by the same man, was farther out to the other side of the building. By the way, that's what I usually do when I arrive early for class - going to the restroom, I mean.

Again, I found the room number arrangements to be weird. What I also found unfamiliar (to me) was that the restroom had a room number. Haha! Then something caught my eye which I momentarily forgot. Then, as I went out, I glanced again at the restroom's number. It read: 5317.

***Flashback***
Man: Where is your class?
Rom: It's 5317 of this building.
Man: What?

Maybe that was why the man was apparently surprised. Or maybe he just heard me wrong. Whatever the case, I mistakenly told the man that my first class in UCLA was in a restroom.