Have you ever found a Leopard frog with a noticeably large tympanum? There's a couple of definite males in the picture below (the one calling and the one on the right) whose eardrums are 'small'. This is the typical size of tympanum for both sexes from my experience wading around breeding ponds

. I'd hypothesize that someone believed since this difference in the sexes was the case for some Ranid species, that it must apply to others (it's very obvious in adult
Rana clamitans for example). That, or the populations near me are abnormal

.