I don't have time to go over the thread - conservative seems dodgy. I'll have to take your word for it. As for your main point, much to my surprise, you're right although I don't understand how, it doesn't match what I've read of it. No matter, you're right.
Boehm disagrees: https://www.hboehm.info/gc/#details
That thread isn't talking about the same thing, which it says no-one volunteered to write.