The reference is outdated. It currently says that closure captures are crate-dependent. https://doc.rust-lang.org/nightly/reference/types/closure.html#r-type.closure.capture.precision.wildcard.destructuring
Enums marked with #[non_exhaustive] from other crates are always treated as having multiple variants. See type.closure.capture.precision.discriminants.non_exhaustive.
However, closure captures are now crate-independent. See rust-lang/rust#150681 and rust-lang/rust#151786