More than likely it is an injury. But one way to determine this is to watch it as the nail grows out. If the spot grows out with the nail - then it is an injury. If it does NOT grow out with the nail, it should be checked.
The one downside to this is that it takes time for the nail to grow and you could drive yourself crazy with worry. But remember that a biopsy on this is not going to be fun. So if you can, let it grow out some to determine if it is an injury or not.
Hoping for the best.