This was back in the time of stack ranking. The performance review he got wasn't just emotionally hurtful or annoying. It actually fucked with his reputation. In a typical stack-ranking regime, performance reviews are part of the transfer packet, actively making it hard to impossible for the employee to fix the situation on his own. While this action was probably overreach, some retaliation is to be expected under such regimes. If a company can't handle that sort of thing, it needs to ditch stack ranking (which Microsoft, admirably, has apparently done).
This doesn't 100% absolve him of responsibility (he still deserves to lose his job over the leak) but it absolves him enough that criminal charges are just inappropriate and wrong for the situation.