To answer this question, simply think about what Wilbur Wright (along with his brother Orville Wright) was famous for. The Wright Brothers were famous because they were the first people ever to accomplish a manned, powered flight. So, these are the first people ever to fly in something that was actually under power (as opposed to a balloon that can't propel itself). If you think about it that way, it makes sense to call him a man-bird. He was a person who did what (up until then) only birds could do -- he flew.
In the NASA link below, you can see a French cartoon of Wright as a bird with a man's head -- it was drawn after the Wright brothers demonstrated an airplane in France.