As discussed way earlier in this thread, we need to read the transcript or hear the recordings to make our own judgement on whether the pilot interpreted the clearance availability to be below 1,000 as a recommendation, or as a direction.
ATC: Mooney you are cleared not above 1,000ft
or
ATC: Mooney, a clearance will be available if you are not above 1,000 ft
Etc etc
This is one of the very few possibilities as to why the pilot descended into terrain on his way to 1,000ft.