Tunguska: Did the aliens do it?

As Ethan Siegel describes in his blog, the weird story of the year award who claims the famous Tunguska impact, 101 years ago, was caused by self-sacrificing aliens putting thier spaceship in the path of a comet to save the Earth. Really. This was reported as news in some quarters. A good comment on the blog asks if maybe the aliens were the ones about to vaporize us, and they were wiped out by a fortuitous comet....