As you can see it is part of Le Mung (https://www.openstreetmap.org/relation/125631) and is reported by Nominatim to be in Le Mung (https://nominatim.openstreetmap.org/ui/details.html?osmtype=W&osmid=61741320&class=place).

You will have to report it to Instagram. They use a different way to give out geolocations. There is nothing we can do on this site.