In training camp, you need a certain amount of players at each position just so you have enough bodies to do all the repetitions that are necessary. If you have multiple injuries at a certain position (say running back), you need to bring in players even if they have no chance of making the roster or even the practice squad. Otherwise, you would overwork the healthy running backs just to make sure all the quarterbacks, wide receivers, etc can get in their repetitions. That is where the term "training camp fodder" comes in. To have a successful training camp, you need a few guys to fill in spots so everyone that will make the team can get their work in.
Coleman and Matthews are training camp fodder.
Fodder (n) - A consumable, often inferior item or resource that is in demand and usually abundant supply