That isn't what it's saying.
/usr/local/share/GeoIP on /var/unbound/usr/local/share/GeoIP (nullfs, local, noatime, read-only, nfsv4acls)
That means /usr/local/share/GeoIP is mounted using nullfs at /var/unbound/usr/local/share/GeoIP
Only the view through /var/unbound/usr/local/share/GeoIP is read only, going directly to /usr/local/share/GeoIP is not read only.