Sorry, I am not familiar with Reddit, I just took the author's word for it:
Anecdotally, that doesn’t be the case with
Reddit’s modern algorithm; comments made
late in the thread appear at the bottom,
where they likely will not receive any upvotes
In my experience with Hacker News, late comments are given some space right at the very top, even if they are a day late. I thought this was a distinction worth commenting on, but maybe I misunderstood the quoted passage.