Well it's not that hard to guess: the famous plumber is of Italian origins, eats lotsa spaghetti, and has been loved by gamers since the 80s - and the 3D shape is perhaps the most known regular solid (but not the simplest possible one), it's so popular even Nintendo named a console after it
Not even that!
Before IOS58, the de facto standard for USB 2 (without using a fully featured CIOS) was a simpler CIOS conventionally installed as 202, while nowadays of course it's official IOS 58 (which thanks to the Wii's modularity, you could install even on an 1.0 console without updating anything else: hell, there's even a dedicated homebrew to do this exact job...)
Unless you want to play a backup of Your Shape, there's likely no practical reason to install a base 58 CIOS
If you think about it, all that "CIOS selection recommended by a guide" means is "CIOS selection liked by whoever wrote it"