The point of that part of the article wasn't that one must wear a polo, but rather one must look professional if one desires to be treated as a professional.
Wearing nice jeans and a nice button-down can be very professional looking. -- wearing torn jeans and a hoodie into a meeting... not so much.
Wearing nice jeans and a nice button-down can be very professional looking. -- wearing torn jeans and a hoodie into a meeting... not so much.