I do not think wheat grass has gluten. Wheat berries also do not have that much gluten, but when combined with water and heat it becomes active. If you eat wheat sprouts you do not get gluten because it is not heated.
One thing nature does is anything that is not whole starts to disintegrate rather quickly. When wheat is whole it survives for a long time, but when converted to flour it starts dieing, the natural process of fungus growth begins, nature's cycle. That is why all old civilizations stored wheat berries with a coating of castor oil and then only made flour and dough as needed and consumed it in a few hours.