What's the right to squat: Focus on driving up and down, or on sticking one's backside out?
From what guys at the gym say, and many pictures online, you need to be sticking yourself out. Yet from Starting Strength's instructions: focusing on tightening lower back, chest up, hip drive - it seems to be more of an up down motion, without as much protrusion. Which is correct? Does the backside need to protrude?
The cue to stick your butt out is intended to help bring your lower back into proper extension to maintain the normal anatomical arch. That means a straight back, not an overextended back.
Actually sticking your butt out can lead to a hyperextended position that is not desirable, but Mark Rippetoe says:
"an inflexible person may need to try to hyperextend just to get to a correct [...] position."
Figure 2-37 from 3rd Edition Starting Strength shows the difference.
So, you are correct, your backside does not need to protrude, but you may need to try to make it do so in order to maintain the proper position.
