Backyard hillbilly car door miracle.

[Will0W783]

Wow, that is interesting. My guess would be that you had scar tissue built up in there that was inhibiting movement that otherwise would have been there. There is some repair and regeneration that can occur in peripheral nervous system tissue (anythign not the brain or spine). I think that even though the tendon was largely destroyed, some of the tissue repaired enough to allow minor movement, but it was inhibited by stiff scar tissue build-up. When you slammed your hand in the car door, you might have broken some of the scar tissue, loosening things up and allowing movement again.
Just an idea.