These guys are probably speaking to each other in words they all get the meaning of. We're a continental country, I think sometimes we forget how close these countries are and how the languages overlap?
It could have been Occitan, the language of southern 1/3 of France, adjoining parts of Italy, and a small part of Spain. It's spoken in Corsica, but I don't know how widely.
The craziest experience I ever had with language was at a party a couple of Nigerian friends were having in college. I didn't have a clue what anyone was saying until I heard the words "fuel pump" and it struck me they were speaking English, but emphasizing syllables in ways we and other English speakers normally don't, while talking really fast. It was an enlightening experience.