If it's not an ILM model, then this is far and away the best imitation of the ILM paint signature I've ever seen on an X replica (it surely is the work of ILM as the site says).
I really like the underside on this one. There's a distinct Chris Foss quality about it, too, in the extensive 'dotting', especially in the pairing of little black dashes on the nose and starboard can. Foss covers his ships in these things, though they first appeared on SF vehicles in Gerry Anderson shows like 'Thunderbirds'. Presumably, since the ILM model team consisted largely of industrial designers and industrial modelmakers as opposed to SF-freaks, elements like this were derived from SF reference handed to them by Lucas. The ESB Falcon is also covered with these marks.