Vegan usually means no products that come from animals. It does NOT mean no protein.(vegan being no protein or anything, just a pure grain diet or not providing proper food for them, like giving them no bugs, insect protein and just oatsl)
Most plant products have some amount of protein. (That's how herbivores like cows can grow: they do need protein, but they get it from the plants they eat. Some kinds of animals digest certain plants more effectively than others.)
A lot of commercial chicken food is meat-free but still provides enough protein for the chickens. The manufacturers use a combination of grains and other plant products, usually including soybeans (which are higher in protein than most other commonly available plant products).
You could read through and and polish it up a bit before posting, if you have a hard time typing things clearly the first time.(I described this badly and its probably confusing