the pothos are toxic to animals because of the oxalate crystals, but in small amounts I have only seen indigestion and mouth irritation. My rabbits and cat nibbled on an entire plant and they threw it up right after and were fine after lapping up water. I would take the pothos out since your frog is getting bigger. I would say you got lucky with such a small piece.
I took out all the plants in mine because he has already taken a bite out of a croton and digs the others up anyways. good luck with the frog recovery