A die chip is where a portion falls away from the die. On this one the coin was not real deep into the die. so the roughness is where the void is showing us how the depth of the void. When the area is flat at the top. the void was so deep, that the metal ran out first during the strike. Example?
This void was so deep that the metal ran out and was unable to fill all of the void. Thus the highest point is level and not rough looking like this chip.