Why wouldn't they paint such a detail on it? If they went to the lengths of painting the aircraft (as opposed to just covering it) then presumably they want it to be credible.

I'm no expert in this stuff but to me the shadow of the plane matches other shadows pretty well, and also the shadow off the side of the hangar is light and looks like the rib structure, rather than solid so the roof is probably not solid. That seems much harder to fake.

You can also see the roof beams over the plane. Although that kind of detail could be painted on or come through the canvass if it wasn't perfectly tight.