The manga is not written by Dragon Ball creator Akira Toriyama, instead it is written and illustrated by (to our understanding) a Dragon Ball fan turned official mangaka named Garow Lee.
This series is titled Dragon Ball Gaiden: Tensei-shitara Yamcha Datta Ken (“Dragon Ball Side Story: The Case of Being Reincarnated as Yamcha”) and re-imagines Yamcha as the hero of the Dragon Ball world.
The world of Dragon Ball just keeps growing, and in this case getting crazier!
With his knowledge of Dragon Ball, this boy trains hard to become the strongest hero in the world.