Stall is due to too an AoA which is outside the boundaries, but stall warnings are in addition due to your AoA being in danger of going outside the boundaries.
If your horizontal velocity is very low you have little lift (even if not stalled) and your downward component of velocity will increase so much that the AoA will go into the stall region.
True.
I think we all have to be very careful to differentiate between the terms "Stall Warning", "Stall Protection" and "Stall".
The first can work to an extent without airspeed data but the second absolutely cannot. So if you get into the first or third in Alternate Law with no speed indication you are going to have to think very hard and work very methodically as quickly as you can.