Cats eat cat grass, why do dogs too?
A craving for unnatural, non-food items is called pica in medical terms. Some dogs just enjoy eating grass, but that does not necessarily mean that they have pica. Some little nibbling is pretty common in dogs (mine does it too), and they seem to enjoy it.
As long as your dog does not start to eat grass excessively there is no danger this little snacking will turn into pica. However, if you notice him eating a lot of grass, quite frequently, consult your veterinarian. No one really knows why some dogs eat grass, it is one of the mysteries of the dog world!
My current dog is the first grass eater, and I had several dogs. I think it is unlikely that there is a reason for dogs to nibble on grass. Maybe they like the taste, maybe they try to settle an upset stomach, we don’t really know.