He's a photographer, so pretty good bet this is a specialist photo inkjet printing onto a suitable paper stock, rather than the run of the mill paper that comes in larger reams intended for more general use like you'd get at the local supermarket or whatever. Photo papers to be of higher quality, thickness (or even be card stock) and weight and do indeed have special coatings, finer fibres, use more cotton/silk, and so on that could explain the texture. Depending on the printer, it might not even be card or paper at all; some support various fabrics, plastic/acetate, and even metal in some fairly specialist cases. It doesn't look like a fabric, but could possibly be a sheet of white plastic/acetate.