I think these fragments were just planted around the site.

If you look at the tipped over trailer next to the crater, you'll see that the "explosion" somehow dug out an 8-foot deep crater and shatter concrete, yet did not manage to deflate any of the rubber tires.

On a somewhat more technical note, air defense missiles almost certainly would not leave any appreciable crater. They are not designed to penetrate or even contact anything, because that is very difficult to do with a fast-moving air target, but just to get near it and detonate, spraying the target with shrapnel.

As a fallback, they may have a contact fuse, in which case it would certainly detonate on touching the ground. Again, shrapnel would just spray around from a surface detonation of a relatively small warhead, leaving little cratering.

So what did happen? My guess would be the Ukrainians in cooperation with the Polish fired an artillery shell, staged the tractor and trailer next to the impact site, and scattered around some of these missile fragments, of which there must be many littering the territory of Ukraine by now.

UPDATE: The US is denying it was Russia, and they're going to go with something like "Ukrainian accident (but really Russia's fault they had to fire it in the first place)". That solidifies it as a UkroPolish joint initiative.

Poland has had a lot of crazy warmongering talk going on lately, and I never see it mentioned but Zbigniew Brzezinski's son is the US ambassador. These maniacs apparently have ideas that now visibly do not coincide with their US/NATO curators.