you did use the word "mild". but it made me wonder if not every person I've ever encountered that looked happy seemed like that a bit.
The happier somebody is the more deluded they look to the rest of us. People in love are perhaps the most obvious. But it says probably more about the observer.
The specific happiness that we're talking about here is contentment -- with your life, with who you are.
I think it looks so odd to so many of us because we tend to be an ambitious bunch, and I find ambition to be pretty inversely related to contentment. The sort of acceptance that this man displays feels like giving up, in a sense. And in many ways, it is -- but that's something that Buddhists have been teaching for centuries.
"Giving up" seems to imply unfulfilled ambition, though. It only feels like giving up because we project our own ambitions onto him. If his ambition always was to lead a simple, predictable life close to nature, he's achieved flawlessly. Maybe I'm just re-stating what you said, sorry.
The happier somebody is the more deluded they look to the rest of us. People in love are perhaps the most obvious. But it says probably more about the observer.