Well, you can definitely interpret it that way, but that's not what Nietzsche actually means to say. He's describing happiness in a universal way, it's an all-encompassing definition of the phenomenom, and what he means by "power" is not exactly what we colloquially understand as power either, though it's not too far. What's interesting here is the dynamic which is expressed in how Nietzsche manages to fuse together his very German-Idealist "will to power" and the Greco-Roman notion of "amor fati". To the begginner, these 2 things might seem totally opposite, but in truth they're complementary.