At this moment, the user needs to force any update. It is okay at the moment as the functionality is basically looking to participant sheets. However even now, it would be better if once day/week the app requested in the background the last participant info.
I guess a little cron job inside a background thread could try to update the app info.
The cron task could be questionned when loading the app in memory (Note: on the iPad and new iPhone the apps have tendency to stay in memory a very very long time) or questionned everytime the app loads the Moodle dashboard (+1 for this behaviour)