by Randy Thornton.
The basic answer is no, the external db authentication method does not push anything, it only queries/pulls data from the designated external source.
Typical solutions to this are - To write something for the other application to pull from Moodle, if you are treating Moodle as your central user database; or to look at centralizing the user data in a system designed to do that using methods like CAS, LDAP, Shibboleth for authentication by multiple apps.
(Not to say you couldn't write something for Moodle to push that data out, but usually applications are designed to poll/pull from a central data source instead of the other way around.)