Tell tail signs:
Grain in the sky, this is sooooooo characteristic of a slide scan, digital grain looks alot different (it looks digital, surprisingly).
The shadow side of the aircraft is not 'clean'. There is grain caused by the darker areas of the shadows, which is also a characteristic in a slide and something you do not get with digital (no grain in shadow areas especially on high end digital cameras). Only digital fault is that everything will be distorted if it is a low end digi-cam, not just grainy.
Most of all, this pic is very contrasty, which would explain the 'digital' look.