@guyjantic Good question. The data for past questions is accessible, if I remember correctly. Might be something for a group of psychologists and a few statisticians to dive in to.
Note: The questions are frequently, but not always, the same. Sometimes it's "How happy do you feel *right now*
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Personally for this specific question: I think it's indicative of the state of mind of people on Fedi.
I frequently select "They are probably happier" because I'm often interacting with people who have moved to France on retirement and are quite comfortable in their lives. I...<ahem>...am not.
Sometimes though, my last interaction is someone who's on Fedi, who I don't know all that well, but the face that I see is generally positive.
Sometimes I interact with someone who is just having the shittiest of days, and I can honestly answer that I'm probably happier.
Any way you slice it, it's my opinion based on what other people put out into the world. A *lot* of people might interact with me regularly and think that I'm happy...I tend to mask well. They may answer the question thinking that I'm happier, simply because I wasn't complaining about my life during the course of that five minute conversation.