Once upon a time, the focus of Dunkey's channel was videos about League of Legends. However, he stopped making them in September 2015. On April Fool's Day of the following year, he posted this video-- which was a video not of the League people were likely expecting, but rather of Rocket League.
The real joke, though, might be that the video is fantastic anyway. It also happens to be a multiplayer video that includes another popular YouTuber, Cr1TiKaL. Dunkey's usual single player style is always great for laughs, but the banter he has with his friends is hilarious as well.