Rinehart, if spelled that way, almost certainly derives from "Rhein-hardt" or "Rhein-herz" meaning "[in the] heart of the Rhein" or "Rheinland" referring to the area the river flows through. This is just a geographical surname, like so many others.
It is also likely that other variations became "Reiner" or "Rayner" and may have ended up as "Reynard" or "Raynard".
It is also plausible, as others have posted here, that Raynard/Reynard may derive from the French "Renaud" or "fox". As such, it MAY (but not necessarily) have been a surname adopted by Jews in that period from 1250 to 1400 when everyone was compelled to adopt a last name for tax counting purposes (what else ?).
Jews were severely persecuted at this moment in time, esp. in very Catholic countries like Spain. Many tried to hide their identity and religious beliefs by taking on "Catholic" names and adopting that religion, at least in public, while continuing to worship in their faith very privately behind locked doors.