Poland Struck...
We can swiftly rule out the S-300 or any other Russian anti-air missiles that have been used as ground attack weapons in this war. Those don't have the range, even if fired from Belarus.
The (single seen so far) impact crater is from a large warhead missile. It's possible that a Polish SAM was chasing the Russian missile and impacted the ground right behind it (that does happen).
It's also possible that the secondary explosion was the stored grain at the farm.
One of the waves of missiles that Russia fired at Syria from the Caspian Sea, almost half of those missiles crashed in Iran.
So I'm not real impressed with any claims of Russian missile accuracy.
I think that the Russians are probably telling the truth when they say that they didn't intentionally fire anything at Poland. But if they admit that their accuracy sucks it kills their defense industry sales.
Much like nobody wants to buy Russian tanks now.
For the moment I'm going to stick with my theory of a Ukrainian S-300 SAM chasing an errant Russian KH-101 into the ground.
It does happen.
US Patriot missiles followed an Iraqi SCUD into the ground in 2003.
