Just looking thru WikiTree entries for each surname, shows that the Caldwell name is much older.
Looking thru that family name, there is a poorly sourced line of ancestry profiles starting in Ireland/Scotland/England which then point towards France with the name of "Calwel" around 1450. With YDNA testing, it may be possible to determine if this is roughly correct or not.
However, as I understand it, the surname "Hughey" is a derivative of Gaelic "O hEachaidh", which means Horseman. So, possibly, a Caldwell at one time may have worked as a horseman and carried forward that distinction.