In the video the knife is a re-textured experience bottle.
Upon throwing the experience bottle, an arrow is summoned and the bottle's Motion tag is copied to the arrow.
The arrow flies directly downward, as if it had no Motion data whatsoever, before quickly teleporting to a spot it would have normally landed if shot normally.
This has only become an issue in the new snapshot, 24w36a.
Attached is also a video on 24w35a, with normal arrow behaviour.