Perhaps he is thinking of how marriage does not change your last name, but rather gives you an extra, optional last name. [1] The French ID card has two last name fields!
Err. It still does by default change your name (if you're a woman). But you can ask and keep your 'maiden' (ugh) name or have both. It gets a bit trickier for kids' family names...
[1] https://fr.m.wikipedia.org/wiki/Nom_d%27usage_en_France