If you are being unkind, then yes he is making what seems to be a type of category error. Dummett or Frege might decribe it as using a second order predicate as

If you are being unkind, then yes he is making what seems to be a type of category error. Dummett or Frege might decribe it as using a second order predicate as a first order predicate. Entirely grammatical, but nonsensical. He probably just means valuable or unique(as a kind of painting whether by authorship or other kind). Title in a previous version might have been "Rare Gottfried Lindauer painting is stolen...", but was shortened.