He answered, “Who made you a prince and a judge over us? Do you mean to kill me as you killed the Egyptian?” Then Moses was afraid, and thought, “Surely the thing is known.”
Yes, normally a Hebrew slave would be afraid of speaking disrespectfully to an Egyptian prince. In this case, the circumstance was not normal. The Hebrew slave saw a prince who was a fellow Hebrew committed a crime against an Egyptian.
Now the opposite was true. Moses was afraid. Of what? Moses was afraid that this slave would report this crime to the authority. Sure enough. It bears out in the next verse:
1 5When Pharaoh heard of this, he tried to kill Moses
Moses was afraid of not the Hebrew slave, but the Egyptian Pharoah.
Why was the man not afraid of Moses, a prince of Egypt?
Because he knew that Moses committed a crime against Pharoah's people and Pharoah was greater than Moses. He expected Pharoah to be on his side against Moses.