The pre-flight checklist should have corrected that error no?
It’s not necessarily on the checklist.
Technically this plane cannot crash into terrain while the TAWS system is working correctly and the plane itself is in good working order and has fuel.
It would either be the pilots ignoring the warnings, the system malfunctioned, or the system was turned off.
Now, it’s possible that with multiple demo flights in the mountainous terrain, that the pilots turned the system off because the warnings were irritating to hear all the time.
They were doing many similar flights to allow the various crews from several airlines to fly on the plane.