That probably says more about the mythological status they had before than about the reality now, but it of course will have an impact on their ability to hire though.
It also should have, and it's normal, and it's how startups turn into big-corps, and that's just the way things are.
The sad truth about culture is that a sustainable culture will feel much more like your parents home than your college dorm; and that will never change... because it's a good thing.
That is the single best line I've read about work culture in software companies in......ever.
I read Github's statement as: "We don't really have any evidence of anything, so we're not going to say anything because we might get sued by one of the involved parties." That situation isn't a good one to be in (and letting an organization get into that situation is serious negligence on the part of leadership).
I'm skeptical. The fact that there is a documented procedure isn't nothing, but it's not that much more than that. I suspect if I went back and counted, a strong plurality of the "I worked in a hostile male environment" accounts I've read occurred in companies with HR departments and explicit sexual harassment policies- GitHub was pretty unique. I've worked in ten-person companies with an HR person.
What an HR department does is make sure management doesn't get sued. The culture of the company isn't something they can control by fiat.