The Ready State Virtual Mobility Coach is like having a virtual Kelly Starrett in your pocket.
I am not an expert at looking xrays so can’t help you there. however, if that is his front view, i would say that his left pelvis is higher than his right. if you lay him down and pull his legs straight, i bet his legs are of different lengths. give that a look. however, i would first test the assumption that it is fixable and not a structural problem.