I can't say whether the metric in the article is good or not. What I can say is that Chicago being comparable to UIUC in CS theory is not an unreasonable position. Across CS it would be false, but Chicago's theory faculty are considered quite good. For example, a few years ago their department housed the only known credible effort regarding P!=NP https://news.ycombinator.com/item?id=1586091. Also, if you look at the two most recent theory hires of the respective departments you'll find them to be of similarly impressive credentials (IAS postdoc, formidable publication record). I don't have the qualifications to really speak more on the subject, but I don't object to the claim.