It's simply a sort algorithm that takes into account any possible signal including OS, Browser, IP / Geo, past purchase behavior, etc. If you figure out that Mac users on average tend to click more on "boutique" hotels that have better design, why would it be wrong to feature those higher up in the results list? It just so happens that those hotels tend to be more pricey but they certainly did not "price" up the same hotel for Mac users. One is standard personalization, the other is price discrimination, and the headline made it sound like the latter.