Probably the reaction is just as fast, but since they add very (very!) small amount of water, when the free electron bubbles collapse and the electrons interact

Probably the reaction is just as fast, but since they add very (very!) small amount of water, when the free electron bubbles collapse and the electrons interact with the H2O molecules the released energy is not enough to cause the usual macro scale effect (the phase change of water to steam, and thus the explosion).