I set the event to Public, and allowed ROLE_ANONYMOUS to watch it. Paella player still requires users to login first. The built-in Theoul player works as designed.
And here is a probable related problem: every time after accessing Opencast series from Moodle LTI external tool, the video can be played without problem with Theoul player (even I set the prop.player to Pealla), the Opencast admin UI cannot be accessed showing up with 403 forbidden for about 10 minutes, then it get self-cured again.
BTW: Wish Theoul player may play videos normally in mobile devices ASAP, then I needn't Paella player any longer.