Anyone can make restaurant reservations. The difference is this:
If you are NOT staying on property, you can book a dining reservation for most restaurants up to 180 days before the dining date.
If you are staying at a WDW resort, you can book dining reservations for most restaurants up to 180 days before your arrival date and you can make them for the first 10 days of your stay.
The primary effect is that guests staying at WDW resorts have an advantage when booking for things that fill up quickly like Cinderella's Royal Table.