I really don't know where the samples came from, that's why I was also asking myself. Even near Genoa there are valleys with villages that have been isolated for centuries. Maybe Angela knows.
If you look at the Corsican paper, it has for some sites less than 5 samples. Obviously that's not nearly enough to use it for percentages. Its probably ok for ancient DNA, if there just isn't more available, but for moderns, its a really small sample size. Even for a rather small island like Corsica.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6070208/