Confidence effects our ability to communicate. Therefore, it makes perfect sense to me that a teacher would be better at communicating ideas if they were dressed in a way that made them feel confident.
I suppose in many ways this is a bit of an empty article. The author really just seems to be saying that dressing up gets people to respect you more, which seems pretty common-sensical. That said, I did find his exploration as to why academics dressed so 'frumpily' to be an interesting one.
I agree with that. Also, if the attire made him feel different, I think it's likely he acted different when he wore it. I'm a pretty casual dresser, but over the years I've tried a lot of different styles of clothes and hair, some that made people confused at times, I think. Back in school I usually had long hair and a wide range of clothing styles. My brother was more traditional, -he wore college t-shirts, etc. For a few days I deliberately dressed like my brother. Almost immediately a girl in my chemistry class (that was a cheerleader, I think) began talking to me. It's just an anecdote, but I do think it makes a difference. I could definitely tell a difference between having long hair and short hair. Some merchants will obviously treat you differently. If a man in a suit or a man in rags begs my pardon in the street, I can't help but have a different idea of what they are going to ask me.
Doesn't that apply to everyone? It certainly works for me. In fact I noticed that even wearing a wristwatch or long hair has a subtle effect; certainly it is manifested in physical ticks. And when you get into piercings and tattoos the effect is very pronounced.