The article mentioned in the original version of the question is not
"Boule de Suif" (which is a novella) but the article
"Les Soirées de Médan"
that Maupassant published in the newspaper Le Gaulois on 27 April 1880.
At the time, de Maupassant was still unknown as an author.
The "soirées" he talks about are evenings that several authors spent at the house of Émile Zola in Médan,
who had by then already published a few works of literature and criticism.
These soirées resulted in the publication of the collective work
Les Soirées de Médan on 17 April 1880.
This volume contained new or reworked novellas by Zola, Maupassant, Joris-Karl Huysmans and three
currently less well-known authors, namely Henry Céard, Léon Hennique and Paul Alexis.
The article criticises romanticism: Maupassant writes that "the works of [Victor] Hugo partly destroyed the works of Voltaire and Diderot".
The sentimentality of romanticism had turned against logic, the old "common sense" and the wisdom Montaigne and Rabelais.
The authors also read stories to each other, which were subsequently published in the volume mentioned above.
Attacking a monstre sacré like Victor Hugo may have triggered criticism, although Neveux writes that it was above all the quality of "Boule de Suif" that contributed to the volume's success.
Neveux writes in his essay:
L'essentiel, disait-il [Maupassant], est de faire «démarrer» la critique.
Elle démarra. Le lendemain Wolff au Figaro polémiquait, entraînait ses confrères. Le succès du volume fut éclatant grâce à Boule de Suif.
The English verb unmoor has a naval meaning,
whereas the primary meaning of the French verb démarrer is "to start" or "to put in motion",
and the naval meaning is now only a secondary meaning.
The Oxford Hachette French Dictionary (French-English, English-French) (second edition, 1998) does not mention the naval meaning of démarrer; its English-French part does not even list "unmoor".
(The entry on Wiktionnaire is based on an older dictionary
that seems to order meanings based on historical principles rather than frequency of usage, which would explain why the naval meaning is listed first. Le nouveau Petit Robert 2006 (which is not as "petit" as its name suggests) also lists meanings in the chronological order in which they appeared.)
The Cambridge English Dictionary also lists the following meaning of "unmoor": "to become less involved with, connected with or influenced by something, or to make someone or something do this". It is obvious that this meaning is irrelevant to Maupassant's article; it is not a translation of any of the meanings of "démarrer" that I could find.
The conclusion is that "unmoor" is an incorrect translation, possibly based on the components of the French verb "démarrer": "un-" matches "dé-", and "moor" matches the French noun amarre (moorings).
The intended meaning by Neveux, however, is that Maupassant wanted critics to start talking about the new book.