As I said in the other thread, "disproportionate" is a disingenuous term here. Blacks also tend to commit a disproportionate number of crimes. So why should their interactions with police be no more than their population proportion?
Do black people
actually commit more crimes or are they just targeted more often by the legal system and so are caught more often?
They actually commit more crimes (of almost all types) and every relevant fact shows beyond reasonable doubt. The more blacks that live in an area, the higher the reported crimes. Suspects are more likely to be described as black by both victims and witnesses in crime reports, anonymous surveys that ask people about being victims of crime show that blacks people are much more likely to be victims of crime and their attackers are mostly black. In addition, there are very official records of crime rates within finite populations where the odds of getting caught do not come into play because everyone is "caught", such as the people who have received court orders to either appear in court, pay a fine, pay child support, etc.. Blacks are more likely to commit each of these crimes.
Then there is the mountain of indirect evidence showing that on countless other variables where blacks and whites differ, those variables strongly correlate with crime rates in the direction that predicts black would be committing more crimes, e.g., income, education level, education and SES of parents, single parent house, SES of neighborhood, and having a prior criminal record (and for the logically impaired, no, that is not circular).
While each of these alone is an imperfect measure, every one of them is far more valid than self-reported feelings of "unjust" treatment by police, and combined they all support the same conclusion and make it beyond reasonable doubt that blacks commit a highly disproportionate % of nearly all "street" crimes that would trigger interactions with the police (in contrast to crimes like tax evasion or white collar crimes that trigger interactions with other government agencies).
Plus, as Trautsi pointed out, it isn't just a matter of the person interacting with the cop having committed a crime. It is a matter of whether they live, work, or hang out in areas with high rates of reported crimes (which blacks unquestionably do). That will trigger more interactions with the police, even when they are not themselves under suspicion. And since many blacks presume extreme near constant racist motives by police, those people would presume that any interaction they every have with a cop was "unfair" and triggered only due to their race. IOW, the OP study is meaningless and measures nothing objective, only subjective perceptions of a vague variably defined "fairness" that is highly influenced by the respondents worldview and presumptions, which we already know differ between blacks and whites.
Oh, and it even worse than that. The study didn't even ask about "unfairness" in general but specifically and only "unfairness due to your race/ethnic background". IOW, they asked people to read the minds of the police they interacted with and infer their motives driving whatever subjectively perceived "unfairness" they thought was there. Not only would a priori presumptions determine the subjective perception of unfairness, but would be THE primary if not only determinant of whether that unfairness was attributed to the unobservable psychological motive of racism.