Chances are he would learn a lot from your buddy. As CC combat training around the world. Is based on Muay thai and BJJ. Instead of taking years to learn it. They get only a hand full of months. They are also taught to kill. While modern day Muai thai and BJJ are not taught that way.
Even when BJJ was invented 100 years ago. Carlos Gracie did not invent it to kill. It was more for self defense. As he grew up in a poor city in Brazil, and his small size. He felt he needed to do some thing to protect him self. With proper training in joint manipulation, pressure, and chokes. The victim could break a bone, dislocate a joint, or choke a person out. In reality the point of BJJ. Is to cause enough pain to your attacker. So that they give up, and run away. Not to kill them.