mechanism of mechanically triggered explosion
There are differing propagation mechanisms for an explosion:


Thermal: a deflagrating explosive such as gunpowder has a comparatively slowly propagating wave-front, depending on heat propagating through the bulk material to set fire to the next layer. This is similar to a candle slowly burning down.
Compression: some brissant (but opaque: see 3. below) explosives create a shock wave. "[High explosives] detonate to produce a defining supersonic over-pressurization shock wave."
Light: fuel-air mixtures, glyceryl trinitrate and nitrogen triiodide explosion can be initiated by light (auto manufacturers are looking at laser "spark plugs" to improve internal combustion engine efficiency). In these types of explosives, light from the explosion itself might propagate a supersonic blast front.


So initiating an explosion through heat alone may initiate just a deflagration, without enough over-pressure to form a blast wave.