I almost cannot believe that a professional ecologist would not have collected that frog for further study.
The fruiting body is protruding from the frog at an odd angle -- forward, instead of upward as might be expected. I suspect that the mushroom is attached to a small piece of wood that penetrated the frog's side following a hard contact. There seems to be no involvement with the surrounding skin or tissues, so it seems very unlikely to be actually growing on the frog.