Tunguska is an incredible event to hypothesise about - the meteoroid airburst is one of the most widely accepted occurrences of that fateful event in Siberia way back in 1908. The untold devastation mimics the effects we later came to expect of an atomic weapon, yet the event happened nearly half a century before nuclear weapons had been officially deployed. What could produce such power, devastation, and how?!
Whilst we could jump into the fascinating conspiracies of Tunguska (ranging from Black Holes, inter-dimensional travel, anti-matter, Aliens and natural gas exhaustion from within the crust), the most unique is as you say, the Meteoroid Airburst scenario.
Within this proposed scenario there are 2 distinctly different variations that you can come across. The first involves the comet/asteroid containing heavy elements - specifically Deuterium (or Heavy Hydrogen, as it is colloquially termed). This was proposed to have created an atomic explosion over Siberia - easily explaining the mimetic visual result of the shock wave with that of a nuclear blast.
Such a blast would be expected to leave a carbon-14 residue, thereby allowing a nuclear event to be realised by scientists later. Sadly, the absence of sufficient nuclear matter directed this theory from 'a consideration' to 'extremely unlikely'. A further revision upon this theory was made by Edward Drobyshevski, who originally put forth the possibility that the event occurred as a result of a Comet passing through Earth's atmosphere, and losing a small portion of it's central 'nucleus'; the remainder apparently vacating Earth before being thrust into orbit around the Sun. This blast would be of pure hydrogen, but of a lower yield than typically expected due to the additional shockwave from the forces involved.
The long-standing belief however, is one held by NASA scientists - a fairly 'boring' meteoroid airburst(!) occured, perhaps similar to the one recently seen in Russia. This involves a high velocity, high mass object which simply generates so much friction with the atmospheric drag, that the temperatures cause uncontrollable expansion of the meteoroid, shattering it explosively. NASA's comments on the process, with purported values are:
"It is estimated the asteroid entered Earth's atmosphere traveling at a speed of about 33,500 miles per hour. During its quick plunge, the 220-million-pound space rock heated the air surrounding it to 44,500 degrees Fahrenheit. At 7:17 a.m. (local Siberia time), at a height of about 28,000 feet, the combination of pressure and heat caused the asteroid to fragment and annihilate itself, producing a fireball and releasing energy equivalent to about 185 Hiroshima bombs."
Despite being a comparatively technologically devoid period of our history, seismometers picked up huge tremors, as far away as the UK; likewise, media sources reacted with gathering eye-witness reports such as the following from a Siberian local:
"Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled."
As much we would love to witness such an event, I would be reticent being anywhere close to the object as it made it's final descent!