Hello, This extension code doesn't access openmeetings database, it uses internal asterisk database AstDB. It is key/value database. If record "open30/room/${EXTEN})}" (where ${EXTEN} is name of calling extension) exists in asterisk database, then extension will be blocked.
Related asterisk database documentation: http://www.voip-info.org/wiki/view/Asterisk+func+db http://www.voip-info.org/wiki/view/Asterisk+func+db_exists