I see a number of subthreads that were all posted 40-41 minutes ago, some with longer comments in them which might be the ones you have noticed. I would bet that these comments were posted before the submission was lifted to the frontpage for a second time. Consequently their timestamps were fudged so that they do not appear to have been posted before the submission time.

If you really care, you might want to ask dang (email hn@ycombinator.com) but I am confident that my explanation is not that far off.