My guess is that some of the logs may have been contained in an older cabin, but that cabin, sitting on a stone foundation on a hillside, is new.
As far as I know, the logs are original to the 1773 and 1820 construction, although it is possible that some of the timber was replaced. I don’t know whether there was a basement for the Bowman House at its original site, but it is highly doubtful that the 1773 structure had a basement.