Of course, the study doesn't address whether those same people would be happy anyway ... I know if i cannot ride, my life goes on, and I keep myself happy, because it is after all, my life, and wasting it being miserable over something like not riding a bicycle would be pretty stupid.
And actually ... Exercise tends to improve physical health. When i wasn't riding to work but was hitting the gym four days a week i was in better shape than I am now.
Another BS study where people draw the conclusions they went into the study determined to prove.