As best as I could tell (IANAC), the paper is looking at the distribution of dark matter halos and how it compares to predictions from our models of the growth

As best as I could tell (IANAC), the paper is looking at the distribution of dark matter halos and how it compares to predictions from our models of the growth and evolution of the large scale structure of the universe (the LCDM model). This model also encodes our limited understanding of expansion. They found less dark matter halos than predicted (with large error bars, though), which means the LCDM model may need some work.