The pocket is the space dissected for the implant. The capsule forms on the inside of the pocket (like a lining) as you heal. If this capsule shrinks, you develop a contracture and distortion and hardness of your breasts. So the pocket is not the same thing as the capsule.
The pocket is the space that the surgeon creates under the muscle for the implant to be placed in. The capsule is the scar tissue that the body naturally forms around the implant while it's healing.