Why do my friends think I'm gullible?

Okay. I was in gym today, and I was talking to one of my friends. I was talking to him about the video game "Skate 2". I had let him play it for a while the previous day. He told me (today) that he had bought the limited edition PC version of the game. I told him there wasn't a PC version of the game. He kept persisting with it, and I kept arguing. Afterward, he called me gullible, and another friend did too. I knew he was joking around about the PC version, but why would he call me gullible? I just don't understand it. Also, he always comes up with these crazy stories, and I never believe him. Why would he call me gullible?