All stalls are caused by angle of attack - I think we can agree that!
Well
The way it was taught to me I have to disagree.
For the "low speed stall" I agree. An aircraft stall at the same EAS 1G (or same angle of attack) at most altitudes, except for the high altitudes where the EAS becomes under the influence of mach effect and the stall speed becomes a bit higher (angle of attack a bit lower).
High speed stall (the way I was taught) is something else. First you get high speed buffet due to shock waves occuring. If you further increase the speed the shock waves become more significant up to the point where there is a significant loss of lift. This loss of lift was explained to us as "high speed stall" or "shock stall" as the effect is similar to the loss of lift due to high angle of attack.
Of course, I am no aerodynamics expert, just the way it was taught to us.