There are similarities, for sure, but "throwaway ticketing" usually means throwing away the complete return part of a journey - i.e. buying a return ticket instead of a one-way, in order to avoid a steep one-way fare.

Throwaway ticketing doesn't require there to be a connection - whereas hidden city does require there to be connection.

(Once a pax disembarks at a point that was not a stopover on any leg of their journey, the "hidden city" element takes precedence. All "hidden city" tickets by definition involve the "throwing away" of the remaining (usually only a final/last) sector(s). "Throwaway ticketing" usually means just not showing up for the return - though it is always better to try and book that return for some future date where it may be of use).