The OT had someone do a close analysis of this gif. It looks like the sword hit his foot and then the preset animation kicks in.
This doesn't excuse the fact that it looked odd, but it might be an issue of hitboxes that are
too good instead of ones that are bad.
Very few other people have experienced this, so it definitely seems to be a special occurrence (which I think supports the foot-hit theory).
Better than DS1 by a mile. People in the OT often complain that the tracking sometimes seems too good.
EDIT: Found the
source after going through 50 pages of the OT fruitlessly.
Damage is dealt on the next frame.