The article is not _just adding an index_. They are embedding one of the search fields in a table _primary key_. That likely means the whole physical table layout is tailored for that single specific query.
While it can help to win this very benchmark it's questionable whether it's usable in practice. Chances are an analytical database serves queries of various shapes. If you only need to run a single query over and over again then you might be better off with a stream processing engine anyway.
The primary key is, in effect, an index. Specializing on the latitude field of a table of geographic data seems like an incredibly small thing to nitpick.
While it can help to win this very benchmark it's questionable whether it's usable in practice. Chances are an analytical database serves queries of various shapes. If you only need to run a single query over and over again then you might be better off with a stream processing engine anyway.