That's the way SPFL will spin it certainly but I'm not sure how the law is something clubs or the SPFL can ignore. He was not self isolating as required. He was breaking the law. The club played him in the game during the isolation period. It's semantics to say there's nothing in SPFL rules that renders him ineligible. The law says he shouldn't have been there and the SPFL shouldn't be ignoring the law in their rules nor think their rules are above the law.
Or put another way, just because there is nothing specific in SPFL rules doesn't mean he wasn't ineligible. Or at least that's the common sense spin.