"I'm a video game buff"

In this quote, Shawn Ashmore is explaining himself as a "computer game enthusiast." This indicates that he is somebody who is very educated and enthusiastic about computer game. He likely invests a great deal of time playing and finding out about different computer game, and might even have a collection of games or consoles. Being a "enthusiast" of something likewise implies a level of expertise and skill, so it's possible that Ashmore is not only a fan of video games, but also extremely knowledgeable at playing them. Overall, this quote provides us insight into Ashmore's interests and pastimes, and reveals us that he is a dedicated fan of computer game.