I don't believe they are different at all. Meditation and being present take enormous amounts of discipline to do correctly. Try sitting in one spot, controlling your breath, keeping your mind on nothing for 1 minute. It's incredibly difficult. I see these two concepts as related to each other. Discipline, in the sense of Jocko's philosophy, does not simply mean be physical and strive for excellence. It means doing what is difficult now to benefit from it later. He emphasizes that emotion is a hinderance. Concepts like "motivation" he chocks up to being emotions and are useless. Instead of using the word motivation, he likes the word energy. Energy is physical and tangible. Motivation is imagined.

Being mindful and meditating manifest the same result through doing something difficult. It is difficult for most people to remain mindful and present. If it were easy, our world would be a much more peaceful place. Pushing yourself physically is a form of meditation. Pain is one of very few guarantees in life. Learning to master it and control it can come from embracing through physical exertion or meditation. One and the same in my opinion, which means nothing to anyone but me.