This study shouldn't suprise anyone. A conservative is a person who wishes to preserve society as it currently is. A person who is content with the status quo has that much more reason to be happy than someone who wishes things were different.
Does this mean that Libertarians are unhappy people? I don't know for sure, because I don't have much observational data. It is not as if Doug Horner and I sit down and talk about our feelings over a cup of chai. But our party is growing, so that is reason enough for me to be happy.
Happiness is relative, though. A man who moves out from under a bridge and into a studio apartment will be happier than a man who is forced to sell his Beverly Hills estate and move into a smaller mansion. Likewise, a Libertarian who wins 8% in an election is bappier than a Republican who gets 41%.