Pay-to-fly is pretty easy to define, it specifically involves the practice of paying for the privilege of occupying a pilot's seat while the aircraft is on a revenue flight with passengers. It's taking away paid work from another pilot. That's why it's bad.
So no, enrolling on a stupid expensive training course is not pay-to-fly. You're not causing another pilot to miss out on a salary by doing those things, you're only hurting yourself.
When people are paying for your piloting services, then you shouldn't be working for free or worse. That's when the line is crossed.