The image posted in the article seems to be the output of some kind of scanning microscope (note the vertical scan lines). Perhaps a 3-channel confocal "optical" microscope, which scans the image separately with red, green and blue laser beams, then combines them into a final image (like a "color" TV image). So it's really a false-color rendering of 3 mono-chrome images (but "true" color in the sense that each beam captures the actual color response of the inks in the printed image (like a TV etc).
The article doesn't mention the resolution of the actual image but, eyeball counting the scanlines, it looks like somewhere around 160x80 or maybe 200x100. With 25,000 dots per inch, that's about 984 nanometers per dot, slightly larger than the wavelengths of visible light (380-870 nm).
The limit of optical resolution is about a half-wavelength, so there seems to be enough headroom left for improving this result.