I wonder if the article authors were thinking of Xerox PARC's offices in Palo Alto's hills? Or the road named "Sand Hill Road" that used to have some venture capitalist offices? Other than those offices I can't think of any significant hill-based offices in Silicon Valley.
Well ... Not a big one, I grant you, but hill nevertheless :
https://www.google.com/maps/@37.4231911,-122.084872,3a,75y,1...