I remember I just had access to internet for the first time somewhere else and looked up at early youtube on some rumors about the next game. Some videos were accurate at least when showing the starters and evil team, the rest of the videos were fakemons or other hoaxes using content from other fangames.
Youtube was still in it's early years, so there weren't a lot of well established poketubers (if any) as far as I remember, it was either some youtuber recording the game with shitty footage, or hypercam2 showing Pokemon ROMhacks like vid related:
https://www.youtube.com/watch?v=qtAWgPGxo5wQuite a lot has changed since then.