I have a lot of random thoughts on this. First of all, it's why I believe so much in Se- it's a skill/ art that most people would take a lifetime to master.
Secondly, I'm not sure if I fully get the methods of how they tested this, but I think it's true no matter which way you slice it. Every psych unit and spiritual theory/ philosophy on happiness talks about being in the present moment, smelling the flowers, etc. Counselors will return you to the present moment- you are not the same as you were yesterday or the same as you will be tomorrow. Being completely today.
I don't think any of us would be on this forum so much if we were in the present moment. (This applies to other life situations as well, most of our days would be much different if we had to be present all the time.) I mean, everything we talk about here removes us. It brings us to our memories experiences, books that we read, new thoughts that we have, something that will happen later. If we were perfectly present while on this forum, we wouldn't be on the forum. We'd realize that we're typing words on the page in the quiet of our houses and want to fill our lives with more exciting things.
It's kind of sad to think about all the interactions that we have on a day to day basis if you consider that most people's minds are wandering a lot of the time. When you're someone listening a story or a thought, you're actually stuck somewhere in the back of your mind, you're not really interacting at all, it's like you're talking out loud but you're engaged within your own thoughts. It makes everything seem so lonely and disconnected. Even if it's something as simple as a social butterfly at the party who is texting/ excited for the future guests to arrive instead of caring for the people who are directly in front of their faces. It's an evolutionary strength but it comes with some serious downfalls. At the same time I guess the necessary things that we "need" to do in life would be really really terrible without having the ability to get lost in your own mind. Or, perhaps "necessary" would be redefined. The wandering mind can also be extremely helpful towards happiness if you are really sick or in a lot of pain physically- or any situation where the present proves to be less than desirable. Either way, it's something to consider- just filling your life with things that will make right now the best it can be.