They've always been hot on who is in France. After a short interval during which the 'Carte de Sejour' was abolished (early 2000s) it was reintroduced and you had to report to the local Marie to register. They knew exactly who was where in France, you could not function there without the documentation. This influx of migrants has stunned them.
Most people don't know that in the mid 2000s France imposed a residency law which effectively withdrew access to social and health services for anyone not born in France. Thousands of British ex-pats were affected (I was involved in our area.) We'd lived there 6 years, registered for tax, received and paid our USSFAR demands (Nat. Ins.) exactly as did French-born residents.
Our rights were withdrawn on the basis that we were foreigners. Try that one for racism! A dear friend comitted suicide because hecould not afford the private health insurance that was then demanded instead. (He also had previously paid into the system.)
France is for France and the French. Anyone who forgets that does so at their and our peril.