What is going on? What is the connection that means working on the feet gives more length to the legs?
The answer is fascia. It is now thought that the body is enveloped in connective tissue - fascia. It is fascia that gives the body its shape. This tissue has "opposite" properties - it can stretch or it can contract. It is like a body stocking - pull on one section and there is an effect on another section. Look at a sweater. If you pull on part of the sweater, you can see a pull pattern going through other parts of the sweater.
Back to the tennis ball trick. By rolling the ball around on the base of your foot, you were stretching the fascia in the foot. Because of the connections of fascia, the release also loosened the fascia in the leg and along the hamstrings. So when you bent over to touch your toes, you found that you could bend over further!
So if a tennis ball can do this, what might a myofascial release session do?