It seems that cargo and crates io use "crates" and "packages" interchangeably. For example, crates io says "Rust package registry". cargo package generates a *.crate file that seems a package (because it can contain some bin crates).
According to this document, a crate is a compilation unit for rustc and a package is a unit for cargo. None of them are uploading/downloading unit.
How do you say "the stuff published to crates io"? I guess it is a package because something like cargo-edit distributes some bin crates cargo-add, cargo-rm etc.