These passages are found in afterwords to the articles “Concert”, “Sonate” and “Symphonie” in the posthumous third edition of the famous encyclopaedia of the arts by Johann Georg Sulzer (1720–1779). They are absent in the editions of the encyclopaedia published during Sulzer’s lifetime, and are presumably the work of Christian Friedrich von Blankenburg (1744–1796), who produced the expanded edition of 1786-87. The passages appear again in the edition of 1798.
By the time of the publication of this edition, Mozart had written five violin concertos in addition to a number of single movements and various other works involving solo violin. In all likelihood, however, Blankenburg is referring to concertos (now lost) by Leopold Mozart, as the passage is probably entirely derived from Johann Christoph Stockhausen’s Critischer Entwurf einer auserlesenen Bibliothek. This volume, published before Wolfgang’s known violin concertos were written, has its own entry on violin concertos and lists all the composers mentioned by Blankenburg, including “Mozart” (466, 660–61). Blankenburg appears to have selected somewhat randomly from Stockhausen’s more extensive list of composers, and probably used the same source for the list of symphonists. Thus Wolfgang is not the “Mozart” who composed the violin concertos and symphonies cited here.
Wolfgang is however explicitly mentioned in the long list of sonata composers, and since there is no equivalent for this in Stockhausen, Blankenburg was at least supplementing his source with additional information, perhaps from publishers’ catalogs.