You may not understand why a satellite would behave that way, but do you understand why an alien spacecraft would behave that way, either?

Most likely, it was very far away and thus you couldn’t see it very clearly. Thus, your mind struggled to understand it and came up with any solution it could. If you were to have seen it up close, it would almost certainly have appeared so different that you could not have believed it was the same thing you saw from a distance, even if it did turn out to be an alien spacecraft.

In short, there is no reason to believe that it was or wasn’t an alien spacecraft. What was it? I don’t know, I didn’t see it. Even if I had seen it, I might not have had a clue. But if you study astronomy and those weird light effects in the sky, you start to grow accustomed to some of the common tricks of the eye, and will likely find these objects to be more easily identifiable.