Some jurisdictions go to great lengths to preserve the original architecture and appearances in older homes. Alexandria, Virginia and Gettysburg, Pennsylvania are two towns that come to mind based on my experience. Manassas, Virginia is one as well. For years they fought the idea of replacing older wooden siding with a newer product like aluminum, vinyl or fiber cement. Since I have seen all of those recently on so many homes, apparently the city fathers have relented on that proscription.
It could be that on stone foundations, repairs with the original material or appearance is no longer an issue either.
The repair on the left was done some time ago. Yes, that is Poly-foam. It was apparently so successful that they used the same product on the repair on the right. It is not the preferred repair.
Poly-foam is a good gap sealer and reacts well against moisture, but the UV rays of the sun cause it to deteriorate. It will turn a darker and darker brown, and begin to disintegrate. Stone foundations are usually very old structures. The mortar between the stones will dry more and more as it ages. As it dries it will crack, fall out or completely release its bond and sit there loosely. Such old foundations should be inspected regularly and repaired, but by an experienced mason with stone foundation experience. Mortar, properly placed, is the preferred repair, for lots of reasons. For all I know Poly-foam is the best repair! That's doubtful though. But for sure, while it isn't the prettiest it may be the most creative!
My recommendation: One of the reasons for buying a historic structure is that it is historic. It is nice to know when people have taken the time or spent the money to preserve that which you intend to buy!