The distinction is the same as if they were seated in a coffee shop. Conversations there are between private people, not with some coffee shop "audience". People who listen in to such conversation, and worse, reacts to it, are doing something which polite people consider very rude.
I don't agree with what Adria did, in that she shamed these guys on Twitter, and furthermore, she's doubled down on some conspiracy theories afterwards. And maybe she has an itchy trigger finger on what might constitute a hostile environment.
But, the issue of hostile environments -- as created through a shared culture of sexualized talk -- that's real. The best intervention I think, would have been to talk to those guys. If she didn't feel comfortable confronting them, she was also justified in taking it to the PyCon organizers.