Well, Grif and the others seem to be saying what a lot of other people have told me, which is that it is not safe to feed goldfish to pacman frogs. I have, however, come across other books and people that have argued the exact opposite, which is that goldfish actually are a good food for pac man frogs...This video was made when I first got my frog, before I knew about this whole debate about feeder goldfish. I now stay away from goldfish, as I think it is better to be safe than sorry.
About the moss as substrate, my frog has never swallowed any of it; he always pulls it out of his mouth. From what I've heard, gravel is what can cause impaction. Anyway, I am going to clean my frog's tank and fill it with eco-earth later on today, as it is time for the monthly cleaning.