It was never 13, that's the entire population, not the ones from that entire group actually committing the 50 or 60 or whatever number it is.

13 = every man, woman, and child within the black population in the USA.

Generously cutting that straight down the middle for men/women means 6.5% are black males. Then you need to close things down even further for the ones from that group more likely to be committing the crimes, so remove the infants, remove most of the elderly, and you get maybe 3%.

So it was never 13/50, it was always closer to 3/50, or whatever the 50 really was.