Oh that one is a classic case of people 'remembering' a rule that never existed - there's a name for this illusion but I forget what it is.
See https://news.ycombinator.com/item?id=16131314 and https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que... for history...
This was (maybe still is) part of "reddiquette." Like the guidelines and case law here, it often found its way into subreddit rules and comments from moderators.
> 'remembering' a rule that never existed
Probably the Mandela effect!
https://en.wikipedia.org/wiki/False_memory#Mandela_effect