A staff member at the zoo said the dog was a companion of the wolf, who happened to be taking a rest indoors when the footage was shot.
"The wolf was alone there because he couldn't get along with other wolves. He was always fighting and getting hurt," the employee was quoted as saying.
Keepers decided to separate the wolf from the rest of the zoo's pack for its own health but the animal grew lonely and "almost depressed," she said.
To keep the lone wolf company, the zoo added two puppies to the enclosure, one of which he bonded with, the report said, adding that the other puppy was taken away.
"After two years they have apparently become good companions," the zoo worker was quoted as saying.
Other footage of the wolf and dog has emerged since the video went online, showing the two playing in the enclosure together.
One clip dated back to 2017, when the dog was still a puppy.
-South China Morning Post