I think he is just trying to give people the diameter, but wasn't sure how to say it. I'm guessing if you stuck in in a square, that square would be 14 1/2 by 14 1/2 touching the edges, but the confusion comes in wondering if he it putting the square in the circle and the measurement is actually corner to corner which would make a smaller diameter.
Someone interested could ask him what it measures across, to help the person out...