You seem to be missing the point. He is saying that the paintings have little intrinsic worth, but gain it from the external circumstance of being created by su

You seem to be missing the point. He is saying that the paintings have little intrinsic worth, but gain it from the external circumstance of being created by such a young artist. Your response that people buy the paintings therefore they have value is completely orthogonal, because that doesn't prove either way whether the value is intrinsic or extrinsic (and art is a market know for extrinsic value, such as a painting going up in price once the formerly unknown artist is discovered, etc).