[tsimionescu]

That's splitting hairs. Restaurants can be fancy or functional, they can serve fast food or slow food etc. McDonald's is a restaurant, as is The Fat Duck.

What they all have in common, and the main appeal, is that they cook things better or faster or with less effort than you would, and they spare you the effort of cleaning up afterwards.

[pjmlp]

McDonald's wished it was a restaurant.

There is a reason why food trucks aren't called a restaurant on wheels.

[tsimionescu]

A restaurant is any place where you get cooked food in exchange for money, and have a place to sit down.

[tomrod]

I think you may be ascribing more weight to the etymology of food trucks than is intended. Most food trucks one finds in small to mid sized urban areas are small, effective restaurants in outdoor dining areas. Absolutely part of the experience.