The explosion looked to be about .2 kilotons (just a guess). An explosion with accompagning fission is more like a dirty bomb or a neutron bomb. It does not have to be enormous to be dangerous and deadly.

There is nothing in any of the footage to suggest the explosion was anything other than a hydrogen explosion, as the official staements have suggested. It CANNOT POSSIBLY have been a fission explosion, or the contamination spread about would have been vastly larger (and absolutely unmistakable in composition).

Fuel-air explosions (of which hydrogen explosions are one type) are among the largest non-nuclear blasts the military makes use of. That looked fairly small compared to some of what the US war machine is equipped to deal out.

http://www.fas.org/man/dod-101/sys/dumb/fae.htm