What exactly are you asking? Most PLers squat with a low bar position because it uses more muscle groups thus helping you move more weight.
It seems the low bar squat is using the back with hold the weight hence the leaning forward, while the high bar squat upright.
What muscle groups are working in he low bar to get the weight down and up?
"When you drop the bar a little lower on your back, you’re effectively decreasing how long the lever of your torso is for the movement. It’s like moving the 25-pound plate a little closer to your shoulder and farther from your wrist. The same basic principle applies to how far forward your knees track. Since they typically won’t track quite as far forward when squatting low bar, that’s also analogous to moving the 25-pound plate a bit closer to your shoulder. That means that your muscles don’t have to produce quite as much force to produce the required torque to overcome the resistance."
http://strengtheory.com/its-time-to-end-this-nonsense-high-bar-vs-low-bar-squatting/
pretty good article explaining it.
To answer your question there isn't much of a difference in muscle activation high bar vs low bar according to the article. Most people can squat 10-15% higher weights at low bar due to the above mentioned torque vs resistance.