All the boards have come off! The foundation now stands on its own. This must be quick dry concrete. It’s amazing how quickly it set!
At this point, it’s starting to make sense and look more like a house and less like a mess of materials dumped in a hole in the ground. An interesting detail I noticed immediately was the fact that the two vertical concrete walls flanking the garage opening have embedded pressure treated lumber. I suspect this is for both expansion (it is well above grade) and for attaching framing to later on.