I'm obviously not familiar with the exact situation, but I'd be willing to bet money that he had received word that it was going to become public and the apology was an attempt to appear proactively remorseful and to circumvent the consequences resulting from the forthcoming publication. (In other words, the "apology" was not the precipitating action.)
This all happened in less than 24 hours. If he hadn't made the confession I'm not sure he would've lost all of that.
To be clear, I can't blame the people who fired him. They probably felt relief that they could finally stop working with him.
As the article said, we shouldn't demonise these men. But that is hard. It's not in our nature as humans. It's hard for us to look with compassion at an aggressor.
He very likely was going to be fired either way; the public apology was likely his attempt to avoid being fired.
From the OP: He was artistic director of a local theatre, and he came under fire from them, which is what prompted the public confession/apology[...]