It was also supposed to only apply if you explicitly went to the subreddit. If you just saw a post in your feed you didn't have to make a post yourself.
But the rule makes the community very very active in a place where there's otherwise not much activity.
/r/196 was a popular sub on Reddit, about 500k subscribers. A lot of them were dedicated users who were very active and had recognizable usernames.
196 was one of the first major subs to shut down and point everyone to the fediverse. It helps that 196 was very LGBTQ-friendly and Blahaj.zone is also very explicitly LGBTQ-friendly, so it was a good match.
196 creates a lot of content because their "rule" was anytime you visited the sub you had to leave an image, whether it was a repost or not. This also works very well for a nascent fediverse where not a lot of OC is being made yet.
Thus 196 was pretty much in the perfect position to become one of the biggest places on the fediverse.
I think they're still down? Not sure, can't check any more. They were my favorite subreddit, so I've been submitting a few posts to the community here also.
Across the fediverse if you stick an @ in front of the 196 it'll work. Lemmy has a thing where they do an ! instead, but that's specifically their thing.