I am not a psychologist, so I'm not qualified to give you a scientific, fact-based opinion on the causes and results of fear. Yoda's words strike me as reasonable, whether or not supported by science.
Consider the following scenario; you, an adult, are confronted by a six year old child who is quite upset. They begin to utter threats like, "I'm going to hit you." Gee, you are twice their height, three times their weight, and infinitely more experienced in just about everything relating to eye-hand control, physics, strength, and power. You are not afraid.
What are the odds that you will punch the little squirt in the face? Zero?
If they were to try a punch or kick, you might reflexively grab or block them, and then proceed to set the bugger down in "the timeout chair" along with a verbal reinforcement of their impending doom.
Now imagine that you had the same degree of superiority in knowledge, coordination, reflexes, and experience in defensive techniques when some average Joe accuses you of taking "his" parking space? At this point our conversation could proceed along two paths; first, why is Joe angry about loosing what he believes was "his" rightful parking space; and second, given your superiority - one might say absolute confidence that no harm will come to you - what is your emotional state, and what are the likely actions you will take.
Again, I'm not a psychologist, but I'm thinking that Joe is afraid of being late, of appearing to be taken advantage of, or of loosing some opportunity. His fear has led him to anger, and if not managed - he could strike out at you. A lot depends on Joe, his emotional IQ, background, personality, and of course how much you participate in elevating the tension.
To the degree that you are an accomplished martial artist, your fear should be minor, if indeed there is any at all. I have been in similar situations and was very surprised how very calm and unafraid I was. Knowing that this random person was not going to hurt me, left me in a much better position to deal with the verbal attack.
Mastering a martial art does not make you more likely to fight. Quite the reverse. Remaining calm in tense situations is a direct result of not being afraid of injury or attack. A psychologist Yoda is not, but fear can lead to the dark side. Mastering a martial art can help you deal with fear, both yours and the fear carried by others.