This is a theory, not fact. that is the dinos, were still around for another 10,000 years are so.
Actually there is evidence that the Dinos were gradually disappearing before the impact because of a reduction in the amount of O2 in the atmosphere.
Other catastrophic events of the time such as the massive outpouring of Basalt Lava forming the Deccan Traps may have had much to contribute to the extinction.
I would doubt that the 10,000 year number is any more accurate than the time or size of impact given that the events were 65mya. Whatever (whenever) these events were, critters that had been on Earth upwards of 100my disappeared in the blink of a geologic eye.