Judging from my experience - restaurants are not. We have started cooking more since the beginning of the lockdown being able to cook during the time that would have otherwise been spent on commute. And we have saved a surprisingly large amount of money in the process.

How could restaurants be considered essential? People can eat without having food cooked for them.

Well... transportation hasn't disappeared. People still drive, cycle and take busses and trains, so clearly these means of transport are essential. However, it is true that air travel has collapsed and restaurants as well, both which seem to be non essential. People don't have to fly to other places (for the most part at least, air freight is still happening plentyfull) and people can cook at home or get delivery, so it seems that not all transportation is essential and that restaurants aren't either.