Yes, my immediate thought when reading this:
Specifically, people were more likely to engage in mood-increasing activities (e.g., play sports) when they felt bad, and to engage in useful but mood-decreasing activities (e.g., housework) when they felt good.
is that it makes perfect sense if you think of happiness not as "something that must be maximized at every moment," but a resource that needs to be rationed or even grown when it's in short supply, but can be expended more freely when it's available. People engage in mood-expending activities when they have extra "mood" to expend.
However, I still think that this misses my point a bit when it says, "They may explain how humans overcome the allure of short-term gains in happiness to maximize long-term welfare." The implication there, it seems to me, is that maximizing hedonism is still the end-goal, but that it's a simple trade-off between short-term happiness and long-term. I don't want to take much time in arguing the point right now, but I suspect it's not that simple. After a lot of thought, I've ended up thinking of the emotion "happiness" as more of a expression of something deeper that we don't quite have a word for, and that deeper thing is what we're all really after.
To keep things simpler, I might instead say it this way: There are different kinds of happiness. One is simple pleasure-seeking and hedonism, another is a more deep-souled immediate sense of "joy" that goes beyond normal pleasure, and yet another is something more like a longer lasting "overall contentment and satisfaction". So anyway, what I suspect this research is really showing is that... well... Imagine you're playing a RPG, and the goal is to build a magic sword that lets you save the kingdom. You have a stamina bar, and when it runs out, you can't do very much. You can't run, you can't fight, you can't craft. The point of the game isn't to keep the stamina bar full, or even to keep it as high as possible as much as possible. It's just a means to an end.
So I would argue that what we normally call "happiness" as an immediate emotional state is like that stamina bar. When your mood is low, you're not very functional, so we find ways to boost it by pleasure seeking. When it's high, we make use of it. But what you're after is not maximizing that immediate emotional state of "happiness". That's just what you do when you don't have enough. I believe our willingness to expend that resource is not necessarily a sign that we are engaging in long-term planning to maximize happiness, but instead a sign that there is some other larger thing, the equivalent of "building a magic sword and saving the kingdom", that we are willing to expend that resource to gain.
I think I have an idea of what that thing is, but it's hard to describe succinctly in a Slashdot post.