Arrows can break infinite decorated pots when falling downwards even when they should have no velocity

There is no velocity condition. All the changelog states is that (impact) projectles now break decorated pots, not that they have to move fast. Change request, not a bug.

If you shoot pots horizontally it only breaks 1-2 pots usually before stopping. Velocity was just a word to describe the bug because I don't know how else to describe it.

That's because the arrow is still hitting the pot before it breaks, removing velocity from said arrow, then the pot breaks, and the arrow falls forward again, and hits the next one, after 2 pots, most forward momentum is gone.
Falling allows it to continue as it simply gets affected by gravity.