The concept is that you could get this data via the linux command line tools,

cat ~/.ssh/known_hosts

will give you the same data. osquery has the advantage of being an agent on box, that will periodically query this for you, and either A.) write the results to disk or B.) post the result data to an endpoint like kolide or doorman. The reason one might use osquery as opposed to shell scripts is simply scale and being cross-platform.