The page describes the postgres user typically used as superuser for a PostgreSQL cluster. It would be useful to add information about best practices concerning the use of this account (or better to avoid using this account) for DB management and application connections.
I'm tending to agree that additional info along those lines is worthwhile to mention; but your comment seems to indicate that you are interpreting this user as being defined in the database when in fact it is the operating system user that is being described.