Re: "grant usage on schema" confers the ability to execute all user-defined functions in that schema, with needing to grant "execute"

grant usage on schema s to z;
revoke execute on function s.f() from z; -- Yes, really!

*This surprises me*

The PG doc on, in the "5.7. Privileges" section at https://www.postgresql.org/docs/current/ddl-priv.html (under "USAGE" following "The available privileges are"), says this:

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For schemas, allows access to objects contained in the schema (assuming that the objects' own privilege requirements are also met). Essentially this allows the grantee to “look up” objects within the schema...

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Is the design of my test-case faulty? Have I found a bug? Or is the doc wrong?