Yes, an easter egg is a secret that can be all sorts of things, usually a detail that makes reference to other sources, or sometimes just something random, out of place from the rest of the game.
It's a cameo of appearence of Mario characters in the form of a "hidden secret"/"easter egg".
I get notifications whenever someone quotes me or rates a post or whatever. So I did see this.
I just want it to be clear there is a distinct difference between a cameo, a crossover, and a reference.
I didn't make up these rules. This is how it really is. A cameo is just a brief appearance by a character that has no impact on the story whatsoever.
So DKVine's friend Roysten making a breif appearancd in Grabbed by the Ghoulies that has no impact on the story is a true cameo, not a spinoff.
In fact the only way it truly would be a spinoff is if Roysten was the main character! Yes a spinoff is when a character from another show or series gets their own show or series. GbtG is not Roysten's own series.