You're right, and that brings up a thought about the picture. They are not really my generation, but I don't think I have ever heard them either collectively or individually be described as "thin" from contemporary sources. In that regard, they were pretty normal sized for the times. I don't know their ages in the photo, but even teen agers today have more fat on them than these adults.
Somebody should put out The Rat Pack Diet. Char-broiled steaks, unfiltered cigarettes, and ice cold Martinis.