Preponderance of the evidence is only used in arbitration, if he's suing then this is litigation. In reality, if he has a contract requiring arbitration or mediation instead of litigation then he has absolutely no power and no chance of winning because arbitratators/mediators are always hired by the company.

Even discounting all of that, the judge/jury/arbitrator/litigator would have to agree that sending him into quarantine and not others constitutes retaliation. To be completely honest, this kind of job is a huge joke. If you take too many bathroom breaks you won't hit your quota and they cN fire you for that.

The only way to win isn't to prove he was treated inconsistently, that can be ignored so long as the reason they stated for letting him go is true.