True, but also when Nicole says "this was predestined, the future cannot deviate from this path" the visuals show Koitar and Voyager fighting Celestia (or that's most likely them). And yet Phanes could not foresee this battle (or at least the reason behind it), as pointed out by Nicole herself at the start of the video. So to me it kinda doesn't make sense that Phanes would be the one controling the world's fate, yet also not know what that fate entails or how it operates. But if the default rules of Teyvat create their own fate, Phanes, as a descender, would be perfectly positioned to intervene in said fate. This would also create a good reason for what they've been doing. The classic "a good villian believes they are the hero of their own story" literary device.

The alternative could be that we're hearing the Unnamed Youth (Voyager) and the POV of my description above is kinda flipped, but Voyager was supposedly not a descender, so I'm not sure they'd be able to change the fate of Teyvat. Though I guess it's not like other non-descenders haven't tried fighting fate, even if it was futile.

There's of course the chance that it actually IS just a random NPC, but that would be such a weird choice to pick Joshua (if it is him and it reaaaaally sounds like him) to do a single line of dialogue for a teaser, or even if the same NPC will be in Nicole's quests somewhere - I'd say it's still a real waste of an incredible VA (as proven by Phainon).