Wheres my weight going? I need help

I'm 5'11 with 15 inch arms, haven't measured any other of my muscle tissue, bench 285, and around 12% body fat give or take 2%. I'm not exactly "small". But I'm only weighing 170lbs. I have friends with arms 4 inches smaller and height 2 inches shorter with less body fat who weigh 15 pounds more than me. Do I have a medical condition I need to get checked out or is there a diagnosis for me? Or am I just an anomaly? Just doesn't feel quite right.