The link Leafo posted confirms we have been using the term correctly. Shadow banning “is the practice of blocking or partially blocking a user or the user’s content from some areas of an online community in such a way that the ban is not readily apparent to the user, regardless of whether the action is taken by an individual or an algorithm.” That Wikipedia page was last updated two months ago.
Itch.io’s team might not want to admit it, but what is happening on this site is shadow banning. It wouldn’t have been if we were told beforehand that our works would be hidden from search results or if we had been individually notified about it.
(I’m still trying to guess if my unindexed pixel art tiles might have been moderated as suspicious or obnoxious. They certainly aren’t “adult NSFW” by the definitions used in Itch.io documentation.)