The aim of Yoga is spiritual liberation, and things like physical health, emotional stability, etc, are by-products. So, in a way, anyone can use yoga in any way they want.
I don't know much about Terry's yoga practice, but I was a bit surprised once when I read a blog post about it, saying that he used to practice Iyengar yoga (a methodology that puts great emphasis on alignment, awaress, sequence, timing, etc) but he decided to start practicing a more fast paced method of yoga (can't remember if he mentioned a specific methodology) because he saw it as more advanced and more similar do swimming. What surprised me wasn't him chosing to practice another yoga methodology but the explanation for it. did. To me it seemed like Terry was approaching yoga in the complete opposite way he approached swimming - considering alignment, detail, etc, more basic then "movement" or "action", without taking into account the concept which I believe separates TI from other methods of swimming: awareness (either in "stillness" or in "action").
But then I remembered that Terry lives for swimming :) He seems to consider swimming his main source of physical, mental, emotional and spiritual energy, so a less polished approach to yoga seems pretty normal.
Actually, it would be pretty normal for any person anyway. I's say the first couple of years of personal yoga practice are like "donkey's work" - you just work hard (this is considering you have some sort of orientation, like a good teacher) And then awareness, orientation, intelligence, start to come. Or they may not come. It may come earlier or later. Yoga is a subjective science.
Believing that, I'd say the most important thing to start a personal practice is having a good teacher, and have perserverance and discipline in personal practice. And from there, it will happen what has to happen :)