There are a couple of possibilities here.

1. He drugged her to the point of nullifying consent and then had sex with her.

2. They got high together, had sex, and then she claimed he raped her and she didn't consent to avoid censure from her parents (who, I'm sure, would have been only too happy to encourage such an account).There was no material evidence or witnesses to prove that the rape happened, however, since she was 13, all they had to prove was that intercourse occurred.

It would frankly be asinine of you to presume to know which one is the case, especially with public discourse so firmly arrayed against Mr. Polanski.

I withhold judgement on this one, but whatever happened, what's going on now is an absurd witch hunt, and he deserves support for that reason alone.

So don't be a self-righteous reactionary. And tell your friend not to believe everything he reads.