Covert surveillance in Afghanistan using a civil registered DA42? Which is then parked in full view of visiting aircraft to be gossiped about on the interweb.
Along with the MH370 conspiracy theory, and the possibility that PPrune mods have some magic way of knowing what is, or is not, an official military secret?
More unlikely things have happened I suppose, but not much.
It'll be doing some variation on calibration / unimportant person transport / surveying work, because that is the only faintly feasible reason to have such an aircraft there.
G