Musk is already in trouble, question is how big the trouble is.
If he’s writing a long and angry article to defend his friend, he must be a close friend to the VC host and it’s unlikely he is not aware of the drug/sex party nature.
If he defends the host when he clearly knows that this host has a well known personal conduct issue, he’s a sexist at least.
When this has become an open secret in his circle, it would be hard to believe that he has no idea of the nature of the party. If he knowingly went to the party, it would be an issue even if he left early.
Since Musk’s name is now publicly related to this story, it would become hard to conceal the truth. If he knowingly defend the host even if he knew the nature of the party, it would still be big problem for a public figure.