not possible to stall swept wing aircraft on the ground
The G-IV incorporates a stick shaker to prevent stall entry in flight (T-tail aircraft need this system). The crash photo clearly shows deployment of both thrust reversers which requires a weight-on-wheels signal indicating that the aircraft had touched down on runway 13.
Based on my own experience in flying all of the outstanding airframes produced by Gulfstream Aerospace over the years it appears on the surface that this accident was caused by a loss of control on the ground. The fact that a 24 year old pilot was part of the crew mixed in with a dead-head flight and a runway width of only 98' may prove to have contributed to this very tragic accident.