I too stopped when I read that sentence. It's like saying someone can't tell the difference in professionalism between someone in a well tailored three piece suit vs. a sweater and jeans until they've been taught.

Ornateness itself is associated with being attentive to detail and likely more wealthy.

And even if you take them at their word, it's a distinction without a difference. Serif is known to be more professional.

But! As many have pointed out, and he does about TNR in the article: the default font for documents tends to suggest apathy. That argument against TNR is just as strong for Calibri. And there are far better looking, more functional fonts than either of these two.