There are no restaurants for dinner located within a walking distance from Benesse House, but there are some casual restaurants mostly located near Miyanoura port.
You can find the list of local restaurants here:
「Naoshima Travel Information Site」- Town-Naoshima Tourism Association official site
Please note, however, that the hotel shuttle bus stops running after 7:15 pm from the Miyanoura port, so if you plan to come back to the hotel after that, you will need to take a town bus or a taxi instead.
・ Bus Timetables:
Getting around on Naoshima | Access | Benesse Art Site Naoshima