It is entirely accurate. The UK parliament is "supreme", and cannot be bound by previous parliaments. This principle is the basis of the UK constitution.
One supreme parliament that governs two countries joined by a political union, both of which have separate legal systems. Which is very different from most "regions", within most countries. Thus why your characterisation of Scotland as just a region is inaccurate.
http://www.parliament.uk/about/how/sovereignty/
Until Scotland leaves the UK, any powers enjoyed by its institutions can be repealed or changed.
Of course in Scotland, the people could choose to be independent, and not be subject to UK parliamentary supremacy.