That seems quite reasonable to me.
What does a kid with a BB gun have to do with this? Nothing, but it "creates the narrative".
Funny, if you drop the quotes, instead of "creating a narrative", the BB gun story actually creates a narrative. Namely a narrative where an ADA is out for blood in one instance of possibly reckless behavior from a child that didn't cause anybody any harm, but ignored another instance of possibly reckless behavior from a child that resulted in the loss of life. Whether this has anything to do with race is of secondary importance. The primary issue is the apparent lack of consistency in the severity of prosecution from this ADA.
If you want to learn more, read about Bayesian probability theory.
Not to get into a Bayesian vs. frequentist debate here, but note that this is not the only interpretation of probability out there. The frequentist interpretation is, in spirit, a statement "in hindsight". Troyusrex's point is that it's meaningless to talk about probabilities of things that are fixed quantities; the frequentist interpretation gets around that by making statements about quantities that have yet to be determined. So one only speaks of probabilities before an experiment has been performed and a measurement made. In practice of course we give things like p-values and confidence intervals based on actual observations, but we interpret all probabilities in terms of an infinite number of identical hypothetical experiments.