I’m sure this will get me thrown out of the “Aliens Built it” Fan Club. But when I saw the picture it reminded me of some of the stone buildings the Vikings built in Greenland.
I’m sure though that when it comes to field stone buildings there are really only a couple of ways to build them. So they would all look similar after awhile.
There are a number of ways to break limestone out of the matrix ~ then you trim it. It doesn’t travel far on horseback BTW, so someone can probably find where the rock came from then measure the weathering and come up with a pretty good date!