There does appear to be something weird going on with that game that you’re no longer linking. It’s definitely marked NSFW (i.e. I can’t find it all all without turning on NSFW content), and it definitely charges money. And yet, clicking on the uberpie tag in the game’s list of tags shows the game, so the game can be found through tags, which should never happen for unindexed games. I am intrigued.
(That the game shows up on the Top Sellers list is no proof either way because that page could intentionally or unintentionally ignore the indexed status of the game.)
One hypothesis is that the game collects payment directly without going through Itch, and that this makes them exempt from the “no money for nsfw” rule, but that’s just one possibility. Another is that it’s a bug on the part of Itch, or an exploit on the part of the game. Or that there are circumstances where browsing by tags will show unindexed games after all.