The GPS information merely tells where the occurence was in the previous period with limited altitude information due to a number of factors.
It does not tell what exactly happened nor does it record the visibility conditions.
I think it DOES tell you, with sufficient accuracy, that the flight path prior to the accident was not one commensurate with taking avoiding action. So, the tailboom severance was NOT a result of an abrupt pull up (following late sighting of a fast jet etc.)
The wording in the report about the GPS accuracy is deliberately conservative - don't forget that instrument approaches are predicated on this system.
As for the throttle, well now you are talking sense. FOLLOWING his loss of control and subsequent descent, he MAY well have operated the throttle in the incorrect sense as a result of instinct and conditioned learning.
Interestingly, Russian helicopters use the the throttle in the opposite sense.