Cosmography of the local Universe

The video "Cosmography of the local Universe" gives a very impressive
view of the positions and peculiar velocities in the neighborhood
of the Milky way.
See http://vimeo.com/64868713# and http://arxiv.org/abs/1306.0091
In this last document there is the sentence:
"Detailed maps of motions are inputs to the translation
from redshift space to physical space and constrain the
underlying distribution of (mostly dark) matter. "
How do they know that most of the matter in our local
Universe is dark matter?

If someone explain to me the following sentence:
"We measure crude three-dimensional (3D) locations from their
systematic velocities and sky positions
(distorted from true positions by peculiar velocities)"
this would be helpful.
Next is written:
" and we can estimate their baryonic masses from their luminosities.
Unfortunately this information degrades with distance and can be
lacking in regions of heavy obscuration. In the case of redshift
surveys, low luminosity galaxies are mostly lost etc"
What this means is that lots of ordinary matter is not observed.
Which is true but again does not indicate that there is dark
matter involved.

Nicolaas Vroom
http://users.pandora.be/nicvroom/