The article is eliding the enum's payload. A more realistic example would, I think, have each leg of the enum contain a distinct type of struct (or some other data) in addition to the tag itself, and then have each EoA factored into its own internal SoA.

These are enums as Rust coined the term, meaning sum types, not as C did, meaning a subrange of ints with magic names. The Spam and Eggs types contain data