If it (cow) has muddy feet, then it must have had a drink.
Watering holes at which animals gather to drink are generally muddy. As a result, it would seem reasonable to assume that an animal with muddy feet has had water to drink.
One could rightly or wrongly be considered as having had involvement in a matter simply by being associated with it. When things are taken at face value, certain conclusions whether right or wrong seem rational and justifiable.