No, I don't think this is an alien spacecraft. It would be just too much to ask of coincidence for the very first detected interstellar comet/asteroid (which we suspect are pretty common) to be an artifact.

Having said that, there are a few things that simply don't add up. We seem to have deduced the shape of this object by its variation in magnitude as it tumbles through space--its "light curve". But I simply can't imagine any natural geological, accretive or collisional process that would create a piece of space rock (or ice) with an aspect ratio of 1:10. And of course, we have no reason to believe an interstellar spacecraft must necessarily be long and skinny, either, like one of our chemical rockets. And if it is an artifact of some sort, why is it moving so slowly relative to our sun, about the same speed you'd expect of any object moving in the general galactic drift? Its moving right along, relative to us, but its motion relative to the Local Standard of Rest (the average orbital velocity in this part of the galaxy) is not too extreme. It also is approaching from the direction our solar system is traveling due to our natural revolution around the galactic nucleus. Just what you'd expect for natural space junk. Why would a spacecraft not have some excess velocity, which is exactly what you'd see if a high-tech somebody launched it with the express purpose of going somewhere in particular?

I propose the fluctuations in the light curve are due to something other than its shape; perhaps it simply is a potato-like rock that has a high-albedo spot somewhere on its surface, say a patch of ice on a rocky or sooty background. Maybe the object is tumbling around its axis, only periodically revealing a dark or bright feature. There is also a possibility that we are seeing two objects, here. A dark and bright one, in orbit about one another. Many asteroids in our own system have proven to be binary, and perhaps an occasional fortuitous eclipse or transit explains this light curve.

I imagine the investigators who have studied this object have examined and ruled out these possibilities, but the published accounts don't bother to explain their logic.

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