why does the random movement of chickens need an answer?
It is inherent in nature for creatures to be curious, at least to some degree, it is most likely a more curious chicken wondered what the big black strip was, walked onto it and then ran across from a car, upon discovering that there was a source of food it decided to stay there, prompting more chickens to cross, but only the more curious one, they remeber this fact and will occasionally cross the road again. Hence why there will always be a small group of chickens on the other side of the road near a free range chicken farm.