Tendons are tendons, muscles are muscles. Neither will convert to the other. Just like it's impossible to convert fat to muscle. You may be able to lower one, and raise the other, but fat will never just become muscle.
The way stretching works in a simple explanation is, if you keep stretching a muscle, it will become damaged just like if you lift weights. The difference is a burn victim or other patient may not have the strength to lift any weight. So by having a patient or assister stretch the muscles and damage them, they heal, just like with weight training. With the healing comes growth; Obviously, weights do more damage and return more muscle, but it's start from nowhere to regain some physyicality.
FST-7 works in a similar way, by keeping the muscles and fascia around the muscle stretched, there is more room for growth. You don't get overnight results with either, but as mentioned, it is step one in a healing process.
Mt Snow, VT - May 5, 2012 - Completed!
Gunstock, NH - June 1, 2013 - Completed!
...i remain, he who remains to be...