light moves fast
Let me rephrase it for you, the light gives zero fucks how fast the source of the object was moving because light is going to light.
"What ever exploded, It was Moving -Fast-" So the flash captured in the cam has not bearing on the speed of the source. Also being a consumer grade camera it probably has a real shitty dynamic range which will not provide an accurate measurement of time due to ccd becoming over saturated from a massive increase in light from the flash in a dimly light setting.