Interesting, but don't understand why they call it a galaxy. A galaxy is made up of stars, but they said this dark matter galaxy object has no stars...so why call it a galaxy then?
The most obvious reason would be that the apparent mass involved is of a magnitude that we associate with galaxies. I would also venture to guess that the theroretical formation process also gives rise to a structure that is similar to a "normal" galaxy (disk shaped with a central spherical bulge). So, it the same mass as a galaxy, and probably has the same shape as a galaxy, and we have no other word than "galaxy" to describe objects of that size and shape, so "galaxy" it is, until somebody invents a new term for it.
I hereby nominate "Phlirgoid" as the new sceintific term for a dark matter galaxy.....