It's not just that he's a professor, it's that he has a PhD in economics. The field of economics itself has given the stamp of approval that he both understands the field and has contributed in novel ways to it.
Kurt Wise has a PhD in paleontology from Harvard and is a young earth creationist. Again, just because someone has something on their resume does not therefore mean that they are correct.
The op isn't using the fact Wolff has a PhD in Economics as a argument that he's correct in everything he says, only that the claim that he "doesn't understand how markets work" is absurd on it's face.
Similarly, saying that Kurt Wise doesn't understand geology and paleontology when he has a PhD in the field and has contributed good science is pretty absurd.
