You touch on the idea, that at a higher level, these methods are all part of the same thing, and that would be true, but it is the approach that makes the difference.It actually can. If they are teaching two different ways to punch, you might get mixed up and do that weird elbow out punch some people do. If one (kenpo) teaches you to get in close and the other (TKD) teaches you to fight from a distance, you could, if you're aware of your fighting style use them as tools when you're close or at a distance, or you could not know which one to do and mess up when you're sparring or fighting.