The fact all people knew standard Franch doesn't signify they were not diglossic or billingual speakers. At these times (1863) patois or dialects were known by rural people in western Normandy (I've a subdialect at hand for N-E Cotentin in Manche) - I've a brother-in-law who know a good bit of Poitevin patois todate, in Ill-et-Vilaine the patois were known and even spoken no long ago in rural areas.
In Brittany, the departement doesn't reflect reality: western parts of Morbihan and Côtes-du-Nord (Côtes-d'Armor todate) were Breton speaking and their eastern parts were patois speaking, so largely more than 50% non French speaking - even in Loire-Atlantique, breton was spoken more or less in the northwestern part close to southern Morbihan at these times and some fishers of Bats and Le Croisic were able to speak breton around 1910 -
Very often until the middle of the 20th Cy, rural pops were diglossic (more than billingual because "patois" or dialects were not learned) all around France and the French spoken in the Center around Paris had some regional taste.
these maps are partly useful but reality is more complicated even if todate these remnants of "patois", dialects and allogene languages (Basque, Breton, Flemish, Alsacian, Thiois (Franconic Germanic of N-Lorraine), Corsican, Catalan) are very weak.
in 1863 I suppose the "French" was still very regional among the common people and not the standard French learned in school or known todate by the media. This in spite of the brutal way the governments used to standardize France language since the beginning of the 19th Cy.-