Strange Scottish Blanket

I have a copy of Burham's The Comfortable Arts: Traditional Spinning and Weaving in Canada.  I love the abundance of photographs and diagrams–the book is a catalogue of a National Gallery travelling exhibition–as well as the curated nature of the collection but because the explanatory text is necessarily brief, sometimes the book leaves me wanting more.  For example, this tantalizing tidbit:

An even stranger survival of Scottish tradition is that the herringbone pattern does not come to a point at the axes of the chevrons but the weave breaks (Diagram 67) making the lines of the twill alternate rather than meet.  This is the way that herringbone twills had to be woven, given the technical restrictions of the ancient warp-weighted loom....[it is] a ghost-like reminder of the fact that traditions survive long after any technical reason for them is gone.

I can see in the photo of the blanket and in the weaving diagram that the herringbones do not come to a point.  I cannot make the leap from that to what I know of warp-weighted looms to figure out how such a loom limits twill weaves.  How would you do a twill weave anyway, how and where would you set up the heddles?  I've only seen diagrams, pictures, and videos of warp-weighted looms set up for tabby weave.  I could guess, I suppose.