Somehow you read the article, but didn't read the article.
This galaxy is very old, but didn't exist during the big bang. That means we had about 500 million years of the stuff that makes up our galaxy to move away from THAT galaxy, before it started producing light.
Think of it this way. You and a friend are outside. He has a battery, and a flashlight. He tells you "Go", and you start running from him. Meanwhile, he has to pull apart the flashlight, put the battery in, and put it back together before he shines it at you. The galaxy (or light) didn't exist during, or at the point of the big bang.