Maybe mention something about how martial arts can be beneficial for any size person with any level of experience and physical ability. Early on, like you said, it seems hard, but with practice and perseverance, anyone can use martial arts.

Also, my experience with karate was that it was more inner work and learning self control than fighting, i.e. katas. The skills help in a lot of situations, and like you said, it only took an arm bar for him to back off. You didn't have to all out attack. He just needed to see you weren't defenseless.