I just checked... not only is it like this on the LG G4, but my Samsung Galaxy s4 is also like this. FWIW, on the lock screen, you can open the Android notifications tray (swipe down from the top), and the volume slider will be there. On the LG G4, tap the left button to toggle mute, vibrate, normal. On the gs4, you can use the volume rocker buttons.
On the LG G4, pressing up seems to bring up the camera and automatically take a picture immediately

I gotta figure out if those are "shortcuts" and how they're binded.