Pacman frogs can be pretty reckless when striking at prey. Tongs can alleviate the worry that they're ingesting something they aren't supposed to, so it's one less thing to stress over. Plus, if you put any supplements on the insects and let them wander the tank, the dust can get rubbed off pretty quickly and they might not be getting the necessary nutrition. There's plenty of ways to go about feeding, my friend feeds her's in a container outside of the tank because that's how he eats the best. Sometimes different ways are better depending on a frog's temperament and personality.