As already mentioned on the extension's page, the username on the Etherpad and the built-in chat can currently be changed by users.
It is therefore currently not be trusted.
To-do:
Implement the correct method to pass the authenticated MediaWiki username to Etherpad Lite using its https://github.com/Pita/etherpad-lite/wiki/HTTP-API mechanism.
Version: unspecified
Severity: normal