You can email hn@ycombinator.com to verify, but I'm willing to bet the charged comment mob flagged it before a mod had a chance to see the post and protect it. This jives with other posts, such as https://news.ycombinator.com/item?id=44277177, being "allowed". The second may have met the same fate, or possibly have been considered a dupe by some users who had already seen the other postings of the same story active.

If you can catch posts you think are unfairly flagged as they happen you can also send them to hn@ycombinator.com. Even if it's a day late they can unflag it, second chance it, and/or watch the comments.

The mods hold a strong opinion that making the moderation log public in some way (so these kinds of things can be seen directly) would cause more problems and discontent than it would solve. I strongly disagree, but I respect that the mods have always delivered satisfactory answers for me when using the emailing process - which is their main counterpoint to the need for a public log.