Also, they don't talk about the things that are obviously driving this. It's not race per se, it's things that correlate with race. If you live in an environment where all black and non-black people have the same distributions of behavior, you won't learn to treat people differently on the basis of being black vs. non-black. It's the fact that black Americans are ~7-10x as violent[0] as non-black Americans that is driving the behavior the paper observes. Obviously. The fact that they don't touch this obvious driver makes them, in my view, cowardly, bad scientists out for a cheap thrill.
0: https://cde.ucr.cjis.gov/LATEST/webapp/#/pages/explorer/crim... 7.5x raw numbers, closer to 10x when accounting for the fact that clearance rates are lower among black offenders (i.e., black Americans get away with murder more often).