A stall seems unlikely as they rather seemed to be going quite fast.
If airspeed is unreliable, it does not matter that it indicates the aircraft is going fast.
Unreliable might mean too hig, unreliable might mean too low, for sure unreliable means neither the pilot nor any speculations should rely on it...
Anyway, the aircraft took of around 90 Minutes after sunrise in good weather. Quite different from Birgenair or AF, there was clear visual reference all the time. Good pilots could handle aircraft under such conditions even after full loss of instruments...
It could be flight controls problem.
Is the 737 max full mechanical controls? Or are there some FBW elements in the control systen which require valid air data to work properly?