It can be said with full certainty, at this point, that this airframe is not the same one that was photographed earlier and released in conjunction with the J-36 photos.
The white/gray airframe, which is pretty evident by now, is the biggest indicator of this, as is the presence of a pitot tube. Unlike some observations made earlier, there does not seem to be a tailsting between the engine nozzles, a further indication that this is a separate airframe.
The most likely explanation that this is an earlier tech demonstrator or prototype that was photographed way before and released just now. Of course, it is also possible that the tech demonstrator might still be conducting flight tests in conjunction with the "full prototype" that was unveiled first.