Humans are most aware of atoms bonding due to the sharing of electrons, but bonding due to sharing of the many other subatomic particles on the move around the periphery of the atom also occur. During explosions, a bonding process begins and does not end until an equilibrium is established. The addition of heat to spark an explosion or compression both result in the same atomic drama - heat particles and other subatomic particles flood a given atom in excess of what the surrounding areas contain, and these particles go on the move. At the point where this wave of motion is traveling outward, a temporary liquidity of atoms is created, as the heat particles form a type of lubricant, so the atoms have mobility beyond their prior state.
Suddenly freed from the prior bonding, atoms on the edge of the wave find themselves free to form new bonds, which they do in accordance with their chemical nature, i.e. their ability to hold subatomic particles such as electrons based on the weight and composition of the nucleus. This new bonding results in excess heat particles, which now do not have room due to the new bonding arrangement, and the explosion process is acerbated. Where the new bonding has been facilitated by the lubrication factor of excess heat, heat particles are not the dominant factor in the new bonding. Other subatomic particles, such as electrons, dominate and dictate the bonding process.
If the chemical mix is such that this re-bonding is just waiting to happen, inhibited only due to the strength of the prior bonds, then it is, as you say, an explosive mixture. This is why certain chemicals or chemical mixes are handled with care, and others are not deemed capable of engaging in an explosion. Those chemical mixes that result in an explosion even without the addition of heat or compression are a mixture of atoms prone to many bonding combinations. They enter the explosion bonding in a manner that is less stable than the new potential bond, which they rapidly migrate to, causing the familiar release of heat and light particles.