He's probably making it up but a stone with this name needs an explanation.
The "Gallowstone" on the top of Cultra Hill marks, no doubt, the place of execution for those condemned to death in the court of the proprietor of Cultra or Balmerino, and in that of the Abbot's Bailie of later times...
Some years ago this stone was greatly injured in an attempt by some persons in the neighbourhood to find treasure under it. It is said to have been previously twice its present size, and to have rested on several smaller blocks of stone; in fact, to have resembled a cromlech. Perhaps its later name disguises its earlier use.
The RCAHMS record says that this is a 'much reduced' cairn, and the gallowstone is probably the capstone of a chamber. The stone is a massive 1.8 x 1.3m.