Sure the hydraulic actuators on the Gnat are hydro boosted. It is a power assisted system, not fully powered controls. The Gnat is an intermediate ex military PtF aircraft as far as the CAA is concerned, making it less restrictive in airworthiness provisions such as the OEM support required if it is complex. Speculation on the reasons is would not be welcome by most on here and the AAIB report will be as comprehensive as any BoI would have been if the aircraft would have been still on the military register. But that leads on that it was a civilian aircraft being flown by a civilian pilot displaying on a CAA approved PDA.