Tell them about it for sure, just to cover your own butt. But it won't affect you in any way, because a) it wasn't your fault and b) it's totally not your accident. But tell them anyway. Covering your own butt is really, really important, especially when dealing with insurance companies.
I've worked in general (home / auto / business) insurance for nearly 20 years, so I know how important covering your own legal butt is. Every one of my customers, including my wife, only signed the contract application after I read every line back to them just to be sure. I did it that way every time because people love to say "my insurance broker never told me about that" whenever there's a problem with their claim after an accident, so I made sure I covered my butt every time. To this day, I've never been sued by a customer. Very few brokers can say that, because they don't cover their legal butts every time.
I don't know much about this I France insurance company, but I do know how insurance companies work and think. And if you give them just one reason, even a minor technical little reason not to cover you, they'll use it without hesitation. If they find just one little detail you didn't provide when they asked, they'll screw you up against the wall and they won't lose a minute of sleep over it. That's why you need to give them all the information they ask for, even if it's information they don't care about.