I don't think someone necesarilly betrayed Joyboy, but they couldn't live up to Joyboy's task, and need Nika's help,
Joyboy said to Emeth "I will save you from the past, hasn't it always been like that?!" in a pose where he may have been happy and laughing,
Edit: Emeth also looked like he was agreeing and he was happy and relieved,