As so often with your posts I was motivated to find out a little more. The content won't be news to you, of course, but Wikipedia has a nice little write up about Kemble's Cascade here
. So, it's just a chance alignment of unrelated stars. Very beautiful, nonetheless.
Coincidentally, it appears, according to this
Space Daily article, that the SEGUE survey
has thrown up a number of new streams of related stars where gravitational tides induced by the Milky Way have apparently shredded a number of dwarf galaxies that got too close.