I think they mean when your retro board has a theme; I've seen various themes applied successfully i.e. sailboat:https://metroretro.io/templates/the-sailboat-retrospective
It's also a way for our team to get together and talk BS, have a little bit of fun etc.
I have teams that respond well to it. People like me, who work in metaphors and abstractions, respond well to it.
That sounds like fundamentalist Scrum.