Actually the studies shows that it is just a big fail...
As there is no difference between the 3 groups which all feel happier and no test sample (so you can't conclude that selfies makes people feel happier, since you have nothing to compare to, since the group which doesn't takes selfie are also "happier"...)
So this studies is completely inconclusive (and a fail), The swiss will be happy to know what happened to their money
If you read the results report, you will see there was a control experiment.
The results can be read here: https://psywb.springeropen.com/articles/10.1186/s13612-016-0044-4
Here is the conclusion from the actual report: