If what surprised you was Figure 1 in the paper [1], note that it depicts only CS departments. The CS department at UW is widely considered among the best in the United States. Not that this is definitive, but it's ranked 6 in the US News and World report [2].
Which really proves nothing since the US News rankings are heavily biased toward perceived excellence, other non-objective measures, and objective measures that have no bearing on how well students are actually being educated. Is there really something so special about UWs curriculum that sets them apart from #20 or #100 or do they just have fancier gymnasiums and dorms and more donations from alums?
The main correlate is the impact of faculty output. This also is not necessarily correlated with the quality of the education students receive. But then, department rankings shouldn't necessarily reflect the quality of the education either.