I'm not entirely sure, something just seems a bit odd. That's why I wanted to check if anyone else was getting the same impression :).
No, it is totally right. You might be confused by the use of the plural of Restaurants. Just like in English German offers the posibility of a plural without articles. That is why it is "in Restaurants". If it were singular it would have to be: Wir haben in einem Restaurant or in dem Restaurant/im Restaurant gegessen.