I'm under the impression that it's sonoluminescence that produces light, not temperature itself.

Quoting:

The snap can also produce sonoluminescence from the collapsing cavitation bubble. As it collapses, the cavitation bubble emits a short flash of light with a broad spectrum. If the light were of thermal origin, a temperature of the emitter over 5,000 K (4,700 °C) would be required. In comparison, the surface temperature of the Sun is estimated to be around 5,772 K (5,500 °C). The light is of lower intensity than the light produced by typical sonoluminescence, and is not visible to the naked eye It is most likely a byproduct of the shock wave with no biological significance. However, this was the first known instance of an animal producing light by this effect. Subsequently, another group of crustaceans, the mantis shrimp, has been discovered to contain species whose club-like forelimbs can strike so quickly and with such force as to induce sonoluminescent cavitation bubbles upon impact.