Its built around Jon Hylands’ Microraptor, both he and I have built AX-12 based smaller versions of this same leg design and it works rather well. We’ve both had it walking and walking well.
It does not use a standard humanoid walking gait, hence the difference in COG placement and wider stance. Feet are actually 5" wide and 7" long, they just appear small due to the perspective. Proportionally they are just about the same size as the bioloid feet. Also, the way its standing in the pictures isn’t a proper stance, the legs are much more upright while walking.
This type of setup would not work well in say, RoboOne style competitions however. Its not intended to take physical hits and relies on a higher COG to walk well.