If the gust existed at all, it might have actually helped since the reason he stalled was the flaps were up and therefore the wing was not producing sufficient lift. A sudden gust of 25 kts would have taken the wing into normal conditions, not caused a stall.
The time difference just doesn't work - the helicopter pulled 95% Tq more than the maximum persistence time measured in the downwash trial before the Cessna got to the roadway 'M'.
Interesting that the Cessna pilot didn't acknowledge his landing clearance (if the transcript of the ATC tapes is complete) - an indication that he was already working at capacity just to land the aircraft, let alone make sensible judgements about other traffic.