A better examination as to its history is to be found at https://landscapeandmonumentality.wordpress.com/2018/03/18/the-boles-barrow-bluestone/ which concludes:
The so-called Boles Barrow Bluestone in Salisbury Museum is the only foreign rock from south west Wales found in Wiltshire not at Stonehenge that can be considered more than a fragment. Yet the archaeological context of the specimen in the Salisbury Museum is uncertain and cannot be considered secure evidence in any argument.
The Boles Barrow Bluestone remains elusive.
The bluestone was sampled in 1990 by the Open University team and the results can be found in:
Thorpe, Richard & Williams-Thorpe, Olwen & Jenkins, D. & Watson, J. & Ixer, Robert & Thomas, R.. (2014). The Geological Sources and Transport of the Bluestones of Stonehenge, Wiltshire, UK. Proceedings of the Prehistoric Society. 57. 103-157. 10.1017/S0079497X00004527.
(Copies of the paper seem to have leaked on line - but I'm not going to link to it)