Yup, John I agree,
From what I know a lot of Hugenots did go to Ireland after the revocation of the Treaty of Nantes (also Scotland, England, and a lot of other places). As far as I know they retained their French surnames which were only mildly angliscised. I cannot think how a French name could become "Caldwell" (other than "Colville"). But Colville was already an established, accepted and recognised "English-Scots-whatever" name well before the Treaty of Nantes and there would be no need for any Colville Hugenots to change their name to Caldwell.
I am far from a French expert but I doubt that a native French speaker would find Caldwell easy to pronounce without some training.