This frog has a tragic past. His whole family was eaten by snakes when he was little, since then he made it his mission to eat every single snake for revenge. He ate this snake infront of the camera because he wants to convey his feelings, it was a way to challenge other snakes.
Actually, I have seen frogs eating snake in real nearly 15 years back in my grandparents home. But that frog was very huge and muscular when compared to the size of this frog.