Most criminologists would be aware that soil evidence on their car could tie them to a crime. And it can. I'm pretty sure that the soils in that little neighborhood have unique markers, as most dirt does. LE appears to think they have tire tracks as well.
Right now, they're going to sample all that dirt, in layers, and reconstruct some of where that car has been. It's possible he got it that dirty in just 3-4 days of travel and that it was (relatively) clean before, but gosh, that dirt really looked ancient to me, as if it had gone through several cycles of damp and dry and was basically baked on there. And I know something about having a dirty car, that's for sure.
LE was checking with local carwashes regularly, so he would have had to organize his own car exterior clean-up (he might have, we don't know). Hard to say about the interior. I would love to see the state of the trunk, but that cheery task goes to the investigators in PA.
I am guessing the car will stay in PA and eventually be returned to its owner(s), but it could provide good evidence that he'd been over in Moscow quite a bit and even specific evidence that he had parked near that house with its specific soil profile. That's bad news for him, on top of everything else.
