To be clear, the claim is if there was earlier community spread, the current virus in France should look different because of presumed mutation rates, because right now it looks similar to China?
This makes me think that either
1. nobody else in France was infected by the spread that they now found to have happened in December, the strain died
2. the findings are wrong
1 seems pretty unlikely. We’ll know once they hopefully sequence and publish the genome of the virus they found.