Multisite vs Single site
WP manages multisite and single site database in a different way. For each site you add to a multisite will add a new bunch of tables to the database.
The plugin does not create different tables for each site like WP does. It just creates a bunch of tables to manage all restaurants, and does not matter if you use a multisite or a single site environment. So you can change between multisite and single site indenpendently without affecting the plugin funcionality.
Use a WP multisite if you want to manage subdomains:
Then for every restaurant you can have different pages:
Use a WP single site if you don't need to manage subdomains and you can manage regular WP pages.