Mach stall is, as stated earlier, caused by the shock wave on the top of the wing causing the airflow to become non-laminar, much like a conventional low speed, high AOA stall. Where the confusion about Mach stall and AOA is creeping in I think is in that AOA will have a very swift and significant effect on the stall - the camber of the wing is accelerating the airlfow over the top surface - we all know that from the first principles lessons. That acceleration brings near-transonic airflow up to transonic, creating the shock wave. At that point, even a small increase in AOA will have a huge effect in further increasing that top flow acceleration and increase the localised Mach number, moving and exacerbating the shock wave and exponentially deepening the mach stall. Reduce the angle of attack ad the effect will be mitigated somewhat, though not eliminated until the Mach number is reduced to get rid of the shock wave entirely.