This scene was shot inside a real restaurant. But it's not named Ruthie's Skillet.
This is the "Spring Street Smoke House Barbeque", a Southern style rib joint
at 640 N. Spring Street, which is just northwest of L.A.'s historic Olvera Street,
and just east of Chinatown, in downtown Los Angeles,
It's also close to another location from this episode: Union Station.
(You'll find the restaurant's website here.)
Here is a Google StreetView of the location.