Pacman frogs are very aggressive eaters and tend to eat whatever is in there way. My frog personally does not eat the cocfiber I have in his cage so I decided to do some research for you.
In the link provided, it states that enough cocofiber ingested can obstruct the bowels. He seems to be knowledgeable since he is in the vet field. PacMan Dies from coconut fiber substrate [Archive] - Arachnoboards . "Young pacman frogs do occasionally suffer impactions from consuming substrate, even one considered safe like coconut fiber. This is especially problematic if the coconut fiber was too dry or the frog was insufficiently hydrated; if the frog was continually inverting its stomach I would think this is a possibility, but just plain overconsumption from clumsy strikes will do the trick as well. Tong feeding, as mentioned, does decrease the chances. Another thing you can try if the frog will not tong feed is simply to place it in a tupperware or bin to feed; some say this is too stressful, but I know many keepers who do just this with their younger frogs sans complications - and it's certainly less stress than being badgered with tongs or getting an impaction from substrate ingestion."

Also surprisingly I find a link to the frog forum (Frog Forum - Pacman and Horned Frogs - Ceratophrys - Care and Breeding ) that states...
"One of the best substrates available is ground coconut fiber. This is sometimes known as coir and is often available under the brand name "Eco Earth". Don't confuse it with unground coconut husk or coconut chips. Pacman frogs can pass coconut fiber if they swallow it during feeding. This substrate has the added advantage of helping to regulate humidity. It's also ideal for burrowing pacman frogs, as long as it is misted regularly. Another often recommended substrate is top soil. Top soil from your garden may contain garden chemicals, pesticides, or parasites which can harm your pacman frog."

I say the best ruling is too much digesting of something that isn't normal pacman food is bad - whether they pass it or not. I think you should either switch to top soil or place your lovely frog in a container to eat that does not have any substrate in it or a damp paper towel. I understand tong feeding doesn't always work but I am sure if you keep him in a little container with crickets for an hour or so he is gonna chomp them up and be super happy and healthy!