How do you explain it?

[Ragnarok-X]

I doubt it is possibly at all. Another species could have a totally different opinion on life. Maybe totally different ethics, maybe research in another way, devoted to religion or something totally unknown to us. I doubt another species will be anything like us. Most Sci-Fi`s, like Star Trek and Babylon 5 are utterly wrong. The chance that multiple species encounter each other, they are all the same size and have the same technology (i.e. metal alloys), and even follow a certain logic or ethic is not plausibel. Another species could, and most probably will follow a different path than the humans did.
Think, it took mankind thousands and thousands of years to evolve into what we are now. There are many path`s to follow.