Everyone's genetics are different. Your friend may hold more body fat in their glutes and thighs, while you may hold extra body fat in your arms or in your hips. We're all different. We're all unique little snowflakes and we hold our body fat in different areas. But, no matter who you are, if you get a low enough body fat composition, we guarantee you that you're going to lose body fat everywhere including your arms.
Starting on the hands and knees, keep a flat back and engage the core. Raise the left leg straight back, stopping when the foot is hip-level and the thigh parallel to the floor. Balance for as long as possible, then raise the bottom right toe off the floor, tightening the butt, back, and abs (try to be graceful here!). Hold for up to 10 seconds, then switch legs.