Its very possible that its implantation bleeding. Try a different brand, even though its uncommon its possible for a test to be a fluke. Or for a certain brand not work well for you.
It's possible, all you can do is wait and see. In a week or so, take another test and see what it says. The bleeding could be a sign of very early miscarriage but for some woman it just happens for no apparent reason. I bled for about a week around the 6 week mark. The docs told me that once I bled I had about a 50/50 chance and I had to wait and see too. But my baby made it, now I'm 37 weeks.