Forgot I was there?

So I was at my SO for the weekend, and his mates came over yesterday to watch a football game, after the game they were doing some uni work in the kitchen so I was just on my phone and joined them in the kitchen after like 20 minutes, they were talking how one of his mates have a date this week etc. I'm with my SO right now and he brought it up and I was like "yeah I heard yous talking" and he just said "oh yeah forgot you were there" like what? How can you forget I was there when I was sitting beside you...