Dislocated kneecap

TL;DR: Kneecap dislocated for no reason, what could've caused this?

I'm a 17 year old male in decent shape (weight about 145lbs). My injury didn't happen too recently. I dislocated my kneecap back in October while I was in Hawaii. The weird part about it though is that it literally happened for no reason. I was relaxing in one of those pool lounge chairs, stood up from it, and right when I put pressure on my right leg my knee just popped out and stayed out for an hour and a half until they popped it back in at the hospital. I didn't pivot at all or anything, it just gave out. I wore a brace for about 6 weeks or so and it's fine now. I only feel an occasional wobble once every couple weeks or so.

I was wondering what the hell could've possibly caused this to happen. I've never had any knee problems before this point. Everything I've read on the internet only relates to trauma or pivoting. If it happens again would I risk serious permanent damage to my knee? The only thing I could think of that may have contributed to it happening was that I began Boxing and Kickboxing a month before it happened. Maybe pivoting on that foot while doing kicks could have weakened my knee?

Really any input or advice is appreciated. Sorry for the long post.