The difference is really history , rather than anatomy or physiology. For most of the history of the spectrum of signs and symptoms now known as patellofemoral pain syndrome, (sometimes known as retro petella syndrome, also known as runners knee, jumpers knee, plica, fat pat syndrome and numerous others) this was thought to be a distinct pathology of the patella and associated ligs. As such it was assigned a name indicative of its perceived pathology.
Since the pioneering work of Australian researcher and physiotherapist Jenny MConnell, these signs and symptoms are generally now known to be a non pathological movement issue known as PFPS.
Those who approach the solution to this VMO recruitment problem from a spinal perspective , know this to be a referred event, where altered patterns of recruitment lead to patellar pressures and irritations and other improper biomechanics of the patella.
These are the result of irritations at the L3 Wikipedia reference-linkfacet joint and its' associated spinal nerve root, leading to these altered recruitment patterns , chiefly at VMO.
For the most part , the old tag of Chondromalachia Patella has been superceded by PFPS , though there remains an inclination in some to see this galaxy of eminently treatable problems as mysterious and therefore requiring somewhat more ponderous epithets.