extra terrestrial - Could the KIC 8462852 (Alien megastructure star) be explained by orbiting gas clouds?

There are some theories to explain that. The following explanations, I took from wikipeda's article.

1. The star has a small companion red dwarf which just crossed its Oort cloud equivalent (at 885 UA). A passing star this close would surely cause havoc and serious disturbances to comets' orbits. This could result in a swarm of comets being thrown into the inner stellar system at once in highly excentric orbits. However, there are severe doubts about this.




2. It was also proposed that a planet with a very big ring system transits the star (or perhaps, nearly misses and just part of the rings transit the star). This is not unprecedent, and was already seen with another star.




3. Astronomer Jason Wright suggested that the star might be younger than it seems and it is still coalescing material around it.




4. Astronomer Bradley Schaefer presented just a few days ago (2016-01-13) a study where he concludes that the star dimmed roughly 20% from 1890 to 1989, and that this is unprecedent for a F-type star. So, there could be still more weird things going on than previously thought.




5. NASA Infrared Telescope Facility found similiarities with another star, Eta Corvi, which is undergoing a Late Heavy Bombardment.

Wikipedia's article also cites another possibility (which took some headlines around the world). But this is just some (unfortunately notable) sensacionalistic (un|pseudo)jornalistic claim that nobody can take seriously:

6. There is an advanced alien civilization building a giant device like a Dyson Sphere or something similarly big.

LocalFluff posted an answer suggesting another possibility:

7. 
   

   The anomalies correlate strictly with the telescope's orbital period and orientation and are obviously a man made artefact because of some unforeseen malfunction of the instrument, nothing astrophysical is involved.

   
   

So, the conclusion (at least my conclusion) is that we simply don't know yet what is happening and we need many follow up observations which will likely tell us a lot. Specially somewhere around May of 2017, when it is predicted that the strange megastructure transit should happen again.

I personally would guess that the close encounter with the red dwarf triggered a Late Heavy Bombardment. But this is only a guess from mine and I have no way to provide evidence for it.