I think the meaning here is that French identity has been formed slowly over time while interacting with the outside. I would be surprised if a group of academics, specially if French, denied the existence of French culture. I suppose some French people find disgusting the idea of having much more in common with a contemporary German (for example) than with a medieval French. I'm not French nor do I follow French politics so just guessing by extrapolating what I know from my own country.