Something about this story didn’t seem right, so I searched back to the original story in the New York Journal News. It was the owner of the dog, not the slasher, who bizarrely told reporters that the dog was racist:
http://www.lohud.com/apps/pbcs.dll/article?AID=20104090349
Everyone one in this story seems a little off if you ask me, but the simple “guy slashes dog because he claims it’s racist” story is false.
Good catch.