It's odd for sure. THere's a few theories out there.

One is that the central nervous system gets stirred up and that it interprets pain more readily from sensations that will not normally produce pain. Look up "central sensitization"

Another could be that your blood flow is being restricted.

My massage therapist thinks its fascia. In my case, I agree with her. There are these little casings that slide over our muscles. THey group them up. For example, a single muscle in my calf might have a fascia, but all the mmuscles in that group would also be encased in another fascia. She says there's a long fascia that runs from the base of the skull down the back, leg, and into the heel. She often finds patients with tightness in the neck will also get heel pain. I stretch out my calves and back and everything running along the line of the fascia and it reduces my heel pain.

For me personally, the heel/sole of foot pain started at the same time as my TOS symptoms, and when my TOS symptoms flare, the heel pain gets worse.