No, it's just the more reasonable. Most likely it's not any kind of artifact, but we have a lot more evidence for the existence of man-made spacecraft than we do for alien spacecraft, and Mars is a lot closer to Earth than it is to anywhere aliens might come from.
Hmmm... I'm not sure we have reasonable evidence either way on this thing. At face value it is a seemingly artificial object where (reasonably) such a thing should not be, and (reasonably) you cannot honestly claim to know where in the universe aliens might come from.
