>>515362786
It did not move to a different finger. It stays on his ring finger until it falls off his hand at the end.
When he is hit, his ring finger is in front of his pinky finger.
The ring's face rotated to face the ground, as you'd expect from gravity.
That would put the side profile of the face in front of his pinky finger. Which is exactly what we see.

It slides down his finger from the shock.
As said, the ring was either oversized, or it was otherwise designed to be easily removed. Like having an open band.