The website also tells use that the ballad was a Manx one. The castle at Carrickfergus was captured by the French under Admiral Thurot and held for 7 days in 1760. SO:

We then have a French Admiral on the Isle of Man writing in English a song about Carrick Fergus to an Irish tune. Doesn't sound quite right to me.

Perhaps if Thurot had stayed on the Isle of Man the English wouldn't have killed him the same year at the Battle of Luce Bay (about 60-65 miles directly east of Carrickfergus). A ballad on Thurot's defeat and death is in NLS MS 12820, to the tune of "Moll Roe", it commmences "The French had thought long to invade us, With flat bottom'd Boats & Bottoes, But all their attempts ne'er afraid us, Like the Squadron of Monsieur Thurot's". It is preceeded in the manuscript by another, "Thurot's defeat Tune of, To all ye Ladies now at land", by Peter Nittle, Esq. [Much later the tune "Moll Roe (in the morning)" was published, but not under it's own title until the following century.]