The expectation value was huge at one point: a few percent probability of hitting the planet multiplied by the enormous cost of it hitting the planet (in terms of life and money and environmental damage).

Risk in this sense is a statistical term for the probability of something undesirable happening. So the risk decreased even though the steroid didn’t actually change its track. What changed is our measure of the odds of the impact.

Even numbers are so six-a-dozen.

But even numbers aren’t primes!