Let me see if I got your question right: You want to understand what causes the meteorite to explode?
Let's explain that in an understandable way.
You know that in space we have nearly an absolute vacuum thus no friction between the meteor and other particles, that's the reason it can achieve such a high velocity without melting down or exploding.Upon entering earth's atmosphere the particle density around the meteorite rises incredibly fast due to its velocity. The meteorite gets a certain resistance dependant on it's speed and size. That's like going out on a biketrip. The faster you go the more air resistance you can feel, even more so when wearing a thick jacket for example, which means a higher surface to attack.
So, the meteor entered the atmosphere and collided with it. Dependant on it's density, hardness and overall energy three things can happen:
It's dense and hard enough to withstand the collision but will have such high increase in thermal energy due to the friction, that it starts to melt down/evaporate "slowly" while moving forward
It has such a high energy and/or small density and hardness that the energy set free is high enough to let the meteorite evaporize or explode directly upon crashing with the atmosphere..
It withstands the thermal and mechanical energy arising and keeps on flying
Of course the meteorite loses energy during that process and will slow down. Note that the energy is not lost but transformed. The air/rocks around the impact will have an increase in energy causing them to thermally expanse extremely fast thus creating a shockwave. This part is what you could call the main explosion.
The explosion of the rock itself is also well explained with this:
"With the meteor moving at this speed, there is a lot of heat generated (compression, as well as friction/viscosity). This boils the meteor (many meteors contain ice or dry ice), leading to a buildup in pressure. If the boiling happens too quickly, the meteor will explode."
The friction increases the farther the meteorite moves so the energy will get higher and higher until the above mentioned happens. This would be a "non-contact-explosion"..
Also the Atmosphere consists of more than one layer of different densities (lower layer, higher density) so the whole process of crashing into a wall of higher density happens several times before finally reaching earth's surface.
In case 3 the meteorite will keep flying until hitting a harder surface, that would be our earth in this case.
The earth is big and hard enough to absorb the energy from the impact. So the meteorite crashes and will then release it's entire internal energy, since it can't move forward anymore, which in most cases is high enough to let it explode or evaporize.. In case of a very small meteorite it might just crash without exploding, because it can withstand the energy, but will still create an impact crater.
So the process when hitting the atmosphere or earth's surface is the same: A change in density causes the meteorite to release energy.
At the end a little metaphor for even better understanding:
You take a rock and throw it against a wall.. It crashes and will maybe create a little crater but it won't explode.. Now you take the same rock and throw it as hard as you can so it has more energy.. when hitting the wall again it will release all it's energy and explode.. Due to the walls hardness it can't move through it, of course unless the rock is is harder than the wall and fast enough.. That would be the equivalent to the meteorite hitting earth.
Try the same mind experiment with the same rock being thrown at water, which would be the equivalent to the meteorite hitting the atmosphere, which can be seen as a fluid.
The meteorite crashes into a higher density wall and the set free energy causes it to disrupt, like a rock thrown at a wall
The build up pressure of fluids within the meteorite causes it to explode
PS: So the release of energy when colliding is what causes the explosion whether it disintegrates or not. The equivalent to 15.000 tons of TNT represents the internal energy of the meteorite that's set free.