Okay I can explain that, the Completonist is a Review type show where each week he 100% completes a Game and reviews it.
The Review is divided up into different sections: the Story of the Game, Presentation of the Game (graphics, musics and the like), Gameplay (basically everything from the meat, mini games and side quest), The Final Level (which can be skipped if you don't want Spoilers), Completion Bonus (Any post game if the game in question has it), The Struggle which I already described, and the Completionist Rating which from highest to lowest are (Complete it, Finish it, Play it, Look at it and Donate it).
So yeah that's why he's explaining the Story in the first 5 minutes, which are mostly spoiler free unless stated otherwise. The Final Level can also be skipped for those who don't want to be spoiled and skips to the Completionist Rating.