Notice how the master's feet are not parallel. His back is also straight while his students' are not. It seems that his hips are a lot more integrated with his thighs too - the base of his spine relatively straight and rooted within the middle of the pelvis when viewed from the side. The knees are above the feet, while the thighs are parallel to the ground. The evidence of his prolonged practice is obvious, especially when you compare him to the students.