So on Saturday an actual moving van arrived. And the same guy was there, and was definitely directing the movers, and with a bit less familiarity than he'd shown with the the tow-truck driver. And at this point, the covered car in the driveway is no longer covered.
So I'm forced to assume (contingently, and also grudgingly) that he's actually just a guy moving into a house, albeit in the weirdest way possible.
I still feel like there's something going on, but now I'm wondering it's much more sordid and mundane than what we'd originally suspected: divorce, maybe, with the husband moving into the former-couple's rental house? Or maybe it's just like I said, and he's just some guy moving into a house in the weirdest and most suspicious way possible.
Regardless, he seems like a decent guy so far.