Looking at the blow-ups, sections of the image that are about 1/50 of thr total image are distinctly fuzzy (OOF? diffraction?) when displayed at less than 200 pixels wide on my screen, so the resolution is well under 10,000 pixels across, making the sample image well under 50MP worth, about 1000-fold short of the headline claim. Maybe the 50 GP refers to some proposed future upscaling: after all, to get 50GP from 98 tiny cameras would need each one to deliver about 500MP.
So I won't believe 50GP on the basis of anything in that article. The calculations of the giga-pixel camera project reveal some of the problems: atmospheric imperfections, diffraction/OOF effects and such make it very hard for any lens to deliver that much detail, except perhaps in an extreme wide-angle view of a subject entirely at a great distance form the camera, so that everyting is adequately in-focus with focus set near infinity even with a large aperture diameter. For normal field of view, controlling diffraction adequately would require an aperture diameter of about 100mm or more; doubling the angular field of view could get that down to about 50mm, and so on.
If you follow the links through to a detailed description of the instrument, it all hinges on one single - rather amazing, but still single - objective lens. I expect that's the limit to overall image quality.