There are three key reasons why this works here.
First, Snapchat filters have a “wow” factor atypical of most features. It’s a social space, so it’s as though one of your friends has magically transformed into a cat — naturally, you’re going to ask questions.
Second, the hidden features are for content that gets shared. A neat feature that only makes changes for one user won’t turn nearly as many heads as neat features for shared content.
Third, these hidden features are not core functions (like taking a photo and sharing it), but are nice additions. I can create and consume content for the platform without ever learning how to turn into a cat.
Most features don’t meet these requirements. If your feature doesn’t satisfy all three of these requirements, you need to make the feature more obvious, as there’s no inbuilt mechanism for adoption to spread.