Thats not an arm, the image shows a profile picture of wrist/hand/fingers, but your point stands.

For reference, use your own anatomy: the bone they use to touch the ground is the middle bone of your fingers (thumb excluded) and the finger tip is curled up. From there we have the finger first bone (slightly bent), hand bone (big one), two wrist bones and just the end end of forearm bone.

The main difference between the two species is how the forearm-wrist, wrist-wrist and wrist-hand articulations are used. Chips bend them and gorillas use then in a straight line.