Sgt. Duffer and the Storm
Agree with LarsG, there are many plausible Sgt. Duffer scenarios that explain this. As he says, fuelling error, or something like a legitimate, but wrong, command and control signal from the US controllers easily explain this.
It is even plausible that a real mission went awry, for example, maybe the drone was deliberately landed in an attempt to re-supply a special-forces unit, but was intercepted by Iranian ground-forces.
Lots of other "natural" explanations work too --- hit by lightning or buffeting from turbulence causing some sort of system disconnection, for example.
If it did crash, as long as it lands in relatively flat terrain a fairly unscathed body is not that surprising either. The drone will probably be designed to glide --- as this saves on fuel for high altitude, long-duration missions. And it is surely designed to be rugged enough to experience a hard-landing without disintegrating into thousands of pieces. It will be designed such that it can land on an improvised/poor run-way when being used by a unit in the field, for example.
On the other hand, it would be foolish to assume that the Iranians hadn't figured out some method of causing a malfunction. And it would be equally foolish to assume that a propaganda statement (from either side) actually contained any truthful information about what this exploit was.