If you are making an approach at 10 kts above the stall speed, and you suffer a sudden drop in windspeed of 20 kts, I assume you will stall.
In many cases I am sure you are right to think a stall would result. But why is quite another matter.
A stall is likely because when the wing lost speed it would loose lift, a sink would then happen, triggering the pilot to instinctively pull back, increasing the AoA and so cause a stall.
But wings only stall due to their AoA getting too high not because the airspeed has reduced below the 'stalling speed' which is a rather meaningless term which changes with weight, angle of bank and manoeuvre and even the power used in some circumstances.