Thinking like an epidemiologist here:
So we have two groups here arguing two different counterfactuals, neither of which by definition can be known in this specific case.
One group is claiming, “Had the student not been black/POC, the Smith employee would not have called the cops”, and thus concluding that racial bias, explicit or implicit, was at play.
Another group is claiming, “the employee was concerned about the student’s actions (i.e., lounging on a sofa in a lounge after a meal in a dining hall in the middle of the day in the middle of the summer) seeming `out of place’ and therefore initiated a reasonable call to security, and would have done so regardless of student’s race.”, and thus concluding that the student (and her supporters) are overreacting and that this is “yet another” case of crying foul or playing the race card without evidence.
So, again, due to the space-time continuum we are currently subject to, we cannot know the outcome of the actual counterfactual: what would have happened had the student been, say, white or Asian? We can, however, construct a credible counterfactual in several ways: One easy way would be to gather a representative sample of similar calls to campus security from a sample of similar colleges. That is, calls to security having to do with someone appearing to be in the wrong place, not belonging on campus, not being a student, etc. but not actually engaged in any threatening, dangerous or illegal activity. We can record the race of the people about whom these security calls were made, and compare this to the racial makeup of the student body or the entire campus community. If the odds ratio for (POC/majority race | security was called while going about daily business)/(POC/majority race| campus population) is positive, large and statistically significant, this would support (not provide causal evidence, I understand that) the hypothesis that people are more likely to call security when the person carrying on the “suspicious activity” is a POC.
It is also possible to simulate similar scenarios in carefully-designed lab and field experiments. In fact, there is a long history and a large evidence base of rigorous work in this space. The preponderance of the evidence very strongly supports implicit racial bias that shapes perceptions of risk and likelihood of taking defensive or offensive action.