Why did this happen to my jeans?

Took off my jeans today to see these at the inseam below the butt area.

But I can’t figure out how or why this happened? And quite frankly I’ve never had a pair of jeans do this. I wear these to work in an office so I’m not like in construction or a heavy duty job, and it’s not like I’m going to the gym with these.

Any way to stitch or patch it?