...well.... I don't know.
At least you're willing to admit it
I don't know either. I say I think they're advanced military, but that's just the most plausible guess I can make. And, its only slightly more realistic than aliens.
There are several dozen examples like this. Wild, credible, and unexplainable by experts. After you've seen enough of them its clear that while some of these might have a perfectly reasonable explanation that no one, not even the experts have considered, they all can't.
I think too many people get caught up in a high school like immaturity of laughing when someone says UFO. Others feel they need to attach a mundane explanation to it, no matter how far fetched, because the unknown is scary. Like the explanation of God is bowling makes thunder less scary to children.
The only thing that is sure about UFOs is that something is going on there for which there is no mundane explanation.