I suspect they might be using voice lines from Chinese gacha games in addition to what clearly sound like VTubers, YouTubers, and Chinese TV documentary narrations. Those games all come with clean monaural CN/JP/EN files consistent in contents across language for all regions, for, an obvious[1] reason.

1: https://old.reddit.com/r/ZenlessZoneZero/comments/1gqmtl1/th...