The step that has a mistake is Step #4. The correct response is:
Step #4 has a mistake. It should say: “Use a straight edge to draw a line that passes through point C (but not points A and B). This line is a bisector of AB¯¯¯¯¯¯¯¯.”
In this step, the line should be drawn through point C, which is the midpoint of the segment AB, and not through points A and B. The line that is drawn through C would be the bisector of the segment AB.