Explainable... not from the information available.
Yes, some are quite easy to have a logical explanation and many are just strange phenomena, like light striking ice crystals in the stratosphere.
But the fact that many aren't readily explainable doesn't lead me to jump to the conclusion that we are being visited by aliens.
Ask yourself this;
If you had the power and technology to travel millions of light years through deep space, and you came to an inhabited planet with vast resources, a diverse population of animal and plant life and some animals that seem to posses at least some level of intellect and industry.
A. land in some remote area and dissect a few farm animals.
B. Catch some of the creatures and stick things up their butts.
C. Just buzz them and freak them out.
D. Go to an apparent population center where the highest level of ingenuity is displayed and make contact. Or at least hang out a while.
Now I grant you that I might do a-c first, but I’m kind of an ass and have a warped sense of humor. After I had my fun I would still do D before departing.