Unless you're suggesting some kind of conspiracy, the author most likely changed their mind and deleted it from their substack...
I used to play a game with myself at predicting which posts I would see in the morning would be removed with in 30 minutes. My favorite example was an article on how important it is to openly talk about the impacts and causes of climate change. It made it to the FP, had lots of discussion and was removed within 30 minutes.
Posts that are likewise seriously critical of the startup world get remove very quickly.
In this particular case I don't think this post is necessarily being censored, but HN does do this very frequently so it's not a crazy question to ask.
A lot of what gets modded is total crap, though, and is low-quality in addition to simply being off topic.
Source here: https://git.eeqj.de/sneak/orangesite
Hacker News is quick to try to remove things that cause flamewars to erupt, yes. For some users this (regrettably) means that any controversial political or social topic gets a flag from them.
In which case what would you suggest, should the mods make special rules that boost content critical of HN, rather than just letting the user votes and flagging play out?