This is along the lines of the recent thread about claimed weights. As Rich pointed out in that thread, the manufacturers usually have a way to defend their numbers.
Here's a few ways KTM can get such a high number:
1) Use crankshaft HP, not rear wheel hp
2) Run it in a pressurized dyno room with extra oxygen pumped in and don't correct for standard atmospheric conditions.
3) Allow a wide range of squish band height and combustion chamber volume on the spec sheet, and make sure that the engine you dyno is at the extreme end of the range for max HP.
4) Special fuel
With the exception of professional riders and tuners, people should stop paying attention to peak HP figures, IMO.