[Verginius Rufus]

Some of those listed are branch campuses--perhaps their best students transfer to the main campus after two years.

It isn;'t clear if they are talking about 4-year graduation rates or 6-year rates. There are so many students who need more time because they are working or have families that a lot of schools track the 6-year figure (after 6 years the number of additional students who manage to complete a degree apparently isn't very high)

[Scoutmaster]

It isn;'t clear if they are talking about 4-year graduation rates or 6-year rates.

They certainly aren't talking about four-year graduation rates. Boise State University has a four-year rate of between 6% and 8%, depending on the source - so it would be in the rankings.