I brought this subject up over at the Straight Dope board last January. At least, the Tesla part. One of the posts mentions an article in a Russian magazine in the sixties that reported that aliens near Cynus 61 had received a signal from the Krakatoa eruption, and sent back a powerful beam, causing the Tunguska explosion.

The end of February, Cecil himself answered the question: What caused the massive 1908 explosion in Tunguska, Siberia? The black hole hypothesis is said to be dismissed as "hopelessly naive."