There is only a logical explanation for this:

Now, speaking seriously, I don't really doubt they're aliens, because the Pokémon series has been hinting a lot this, Deoxys is an alien, Clefairies can build spaceships in the anime. Now, after years of enduring humans, aliens have decided to settle the score. I don't think it's not impossible.

I really want to catch these UBs even if they're the end result of an unethical science experiment. It's not like it would be the first time.

I need glass jellyfish, sass bug, and buff tick on my team.