It's not really clear they can pinpoint any actual discrimination, just that this platform isn't statistically recommending certain ethnic groups at the same rate as distributed interviews. though seems there could be tons of conflating factors there.

though I did turn up this from the paper

>pymetrics. pymetrics builds 16 online games to measure applicants’ cognitive traits, including propensity to take risks, processing speed, trust, altruism, and planning ability. For each client, pymetrics trains a binary classifier: positive training examples correspond to the gameplay features of at least 50 current employees in that role and negative training examples correspond to the gameplay features of random profiles in the pymetrics database [46].4 Choosing which employees will serve as the positive examples is the primary way that the employer influences the classifier

https://algorithmichiring.github.io/paper.pdf

Seems possible that this could create bias towards the existing ethic makeup of a position. if the existing employees are predominantly white males the games may subtly bias against any out-group