If you believe it is a probe you must assume an alien civilisation.
Occam's Razor suggests fewest assumptions win.
Supposedly it accelerated a bit, inconsistent with what we know about how rocks move through space.
No decision needs to be made. We don’t know if it’s a rock or anything else and that’s ok.
The basic weirdness is this: it didn't move like a rock, and anything normal that outgassed from it would have been visible, but it wasn't.
There have been a couple hypotheses for weird things it could have been made of, but those ideas look unlikely for their own reasons. One for example was that it was frozen hydrogen, but that would have evaporated in interstellar space. The earth has not shattered because most people assume there's a reasonable explanation that nobody's figured out yet.