In La comtesse Greffulhe, l'ombre des Guermantes, p. 382 Laure Hillerin suggests the possibility that this could have been written by Proust on the request of Comtesse Greffulhe. "One thing only is certain: a long report about the party appeared the next day in Le Gaulois, under the signature "Tout-Paris" - the very same that he had used in 1894 in the same paper, about Montesquiou's party at Versailles. By its style, its erudition and its content, this article, which praises Wagner, has some Proustian resonances: but the signature, which was a collective one, gives us no definite proof."
The lengthy excuses Proust made to Comtesse Greffulhe for not being willing to write the article (Corr. IX, p. 140-142), the very length of the article itself, and the lack of evidence that Proust actually attended this event make it very unlikely that it could have been written by Proust.