How does exaggeration add humor to stories?

It's like the time I went fishing and caught a catfish that was 300 pounds. I actually had to call in a crane company to lift is out of the water and then get a moving company to bring it to my house. It was so big that we had to remove the front door to get it in. I was so hungry after all that work that I ate the whole thing that same day. I put on so much weight that I had to go to Weight Watchers. When I got there everyone stood around and watched. Really this is a true story.