My primitive understanding of explosive mechanics, gleaned after the Boston Marathon bombing, is that explosions can consist of 3 things: smoke, light, or energy. Slow explosions produce a lot of smoke. Like the conflagration of SpaceX's AMOS-6 static fire test that resulted in a destroyed rocket and payload. Or the Boston black powder pressure cooker. Smoke generation is usually a symptom of very imperfect combustion, starvation of oxidizer, I think.
Supposedly nuclear explosions generate a lot of light. Don't know, never seen one and hope never to. Fireworks also generate a lot of light, as does magnesium or phosphorus. So chemical sources can also generate light over smoke. Unsure of the "why" of it.
This explosion was a near perfect sphere of energy with very little smoke. I've heard that C4 and other similar military grade explosives are extraordinarily efficient in producing energy with minimal smoke and light. I was worried at first watching that I was seeing a nuclear explosion from the perfection of the sphere, but it appears to halt at about a 2-3 block radius or so. And didn't appear to knock down buildings inside that 3 block radius, other than possibly the source building.
ETA: Wow, watching it a few more times, I see shards of buildings 3 blocks away getting broken off and lifted into the sky. Big pieces, several feet square, accelerated pretty fast. This is the view from an apartment building probably a mile away or so, and elevated. And the neighboring big white building appears to just get FLATTENED by the shockwave.
