That's a bit upsetting. I would not have expected that fabric to moire.
A pattern of tiny specular highlights? Can happen with glossy, synthetic fibers. Tiny points of light smaller than a pixel alias/moire very easily without an AA filter, and there is no way for conversion software to remotely guess if it is color or luminance information. If it is blurred enough that it affects neighboring red, green, and blue pixels, then it is more clearly luminance information.