Camera button functionality on Lock Screen

One day, while I was putting the phone into a bag, I must have accidentally hit the Camera button as I was inserting it into the bag; the camera turned on, and I guess it STAYED ON, and when I came back 5 hours later, the battery had drained to almost nothing, even though it wasn't recording anything, on the Video mode that it knew from being used the previous time.

How is the OS so advanced and technological, yet it doesn't know to switch off when it's not functioning, after about 5 minutes of nothing being recorded????

Is there a way to prevent this from happening? A function where it knows to switch off the screen and go to sleep after a few minutes of non-use from the camera being turned on by accident from the lock screen???

Thanks