The answer to your question is who knows? An artifact is something that introduces "noise" into the equation and translates into something that is seen on the MRI image. It is not consistent. This means that it would be seen in one plane (like the saggital or from the side) but not in another plane (like the coronal or transverse).
It is most likely just noise and not a lesion.
Quix
Yes, it could - but it's hard to say without the exact wording. When they say artifact, it's because they don't know what it is.