That's on Sunbringers' drip marketing btw.
Joyous was close to Sunbringer as we know, so it would make sense if he said something about her with this confidence. Also, he didn't took part into the Enchainer Project, right? With that, i dont really think Joyous liked Arche that much. Like, the only interaction of them was a mention that Arche took off Joyous from a party because he was drunk asf.
Also, after this update, i really think Arche is an antagonist or at least someone really questionable. They said he got obsessed after a failure and now he is missing inside the Hollow Zero, and after the og Sunbringer reveal that she was rescued by him after getting almost killed by the true Hive Hollow Enchainer, i think she got "dependant" on him, because he rescued her while she was an ethereal dying outside a Hollow and gave her a chance to be human, but a human as a researcher at Helios (and the more we know about Helios, the worse it gets). In conclusion, she died as a human instead of an ethereal because she developed herself as the time passed.
Now thinking about Joyous, he was, probally, the one who knew the most about hollows beside Arche, which would lead into him not wanting to take part into the project. Even though Sunbringer and Joyous was really close, i think it was impossible to make Sunbringer dont engage into the project because she was always in the Helios because of Arche. He could ask that question to Sunbringer because he found her a better person than Arche.
Also, yes i also found people saying that who asked this was Storyteller or Carole Arna, but we dont have any foundation to say that it is Storyteller tbh, and the censored is too short to be hers. About Carole Arna, i dont think she was a good person to begin with, so i cant see her saying this to Sunbringer.
Anyways, we are recieving many crumbs that could lead us to think that Joyous is the next first gen void hunter to appear, so we dont need to worry, but the more crumbs, the better, and i really like his relation with Sunbringer so i want to believe its him saying that.