It's more the norm for adult chickens to give chicks a hard time than it is for them to be indifferent. It also depends on the age of the older chickens. While chickens who are several years old tend to be indifferent to new chicks, young hens and pullets tend to be bullies.
I recommend the panic room method of integration, using a safe enclosure for the chick that provides safe refuge where the older chickens can't get into, but the chick can get in and out of if it chooses.
As the chick grows, food and water can become a difficult issue since the bullies will try to keep the chick away from them. So the panic room contains these essentials during the crucial growth phase.
You're very fortunate the flock didn't kill the baby. That is what usually happens when a chick gets out among the flock while it's still much too young. I don't let my new chicks mingle until they're three weeks old and have been learning and observing the behavior of the older chickens for a good while so they understand the inherent dangers.
Read my article on outdoor brooding linked below this post. it has pictures of my panic room setup and how I go about integrating my chicks.