Jet set casual = sprezzatura.

See Luca Rubinacci (Rubinacci of Napoli) for reference.

Thin

He'd look good in anything.

I think you are overthinking this. As you already said People working there are working with tourists who came there to relax and are probably not thinking about dress codes as they would if they were not on a vacation. I'm sure they won't refuse to serve you no matter what you wear.

We once owned a fine dining restaurant, not pretentious in any way. Great food, local, often organic, from scratch, reasonable prices. it was part of a large inn (or hotel), so we were okay with the food service breaking even. There was another inn in town that had a very, very pretentious and expensive place. We had many well-travelled people say our food was better, but the other place outdid us on the phony baloney, marketing, press, over the top presentations and exaggerated menu descriptions, etc. When I see terminology like “jet set casual”, I can only say “gimme a break”. They aren’t ranked high by places like tripadvisor, but you liked it, and that’s all that matters. The dress code may be a diversion to make diners pay less attention to the prices or even the food itself. Enjoy the view, the food and your family and forget worrying about the dress code. Some people even wear shorts on jets.

Although apparently you can't just wear a bra, sorry "crop top":

https://www.dailymail.co.uk/femail/a...s-Morning.html