Why would it look like a rock? And if it was sent, why wasn't it closer? Might as well claim that God put it there. If it actually was aliens it's quite likely that it wasn't sent specifically for us.
Here is a lot more information. It accelerated when it got close to the sun and then decelerated. Seems like a natural phenomenon of being pushed by strong radiation from the sun.
It entered the solar system at a speed of around 23km/s. That's painfully slow to actually travel through space and bridge any kind of distance in a reasonable amount of time. You need hundreds of years to get through the solar system at that speed let alone get to it from somewhere else.
From what i read at the start of the week the issue they had was that it decelerated when it should have continued to accelerate if it was an actual object like an asteroid.
Also one conclusion was that it wasn't an active alien sail but rather one that was discarded and it just kept on floating through space as the object did not appear to have any active frequencies (well ones we know about) to scan our planet.
In any case whatever it was by the time any information has been relayed back to alien base we be long gone lol.