I think the point being made is that if instead at looking at the wording of the rules, they look only at employee pay and employee premiums, it could be that f

I think the point being made is that if instead at looking at the wording of the rules, they look only at employee pay and employee premiums, it could be that fewer of the lower paid employees got vaccinations, and thus paid more on average. That might make them culpable even if the rule wasn't inherently biased. They have made a lot of rules like this recently, such that an uneven outcome puts you in breach of the law regardless of the fairness of the policies.