My last company punished a guy who was accused of some sort sexual harassment by a woman, and they wouldn't tell him who, when, or what the details were. He seemed genuinely confused what it could have been.
It's entirely possible that everyone involved knows what's going on, and he's just trying to save face. People do that sometimes, after they misbehave.
Happens all the time, FAANG firms are constantly getting in trouble for it.
One difference between a courtroom and a workroom, is that a boss can often ruin his accuser's life in the latter. The justice system works because it treats all people as equal. In the workplace, you are not the equal of your manager.
Fortunately, you can always escalate your complaint into a courtroom. Unfortunately, proving retaliation is next to impossible.