Several commentators have guessed that the "foreign money" in the song had to do with Confederate vs Union currency, which doesn't fit the time-line of the theory I believe, which has the narrator living in New Orleans more than 20 years earlier.

Back in the 1830s (and even later, through the Civil War), there was no standarized nationwide paper money ~ different local banks issued their own bills, hence the word "banknote." The proliferation of different-looking dollar bills may have looked confusing to a newcomer used to life under the more-tightly-organized British crown. Or maybe banknotes from one's hometown bank were not recognized once you traveled out of town, requiring the traveler to go to a local bank to exchange currency.

(Aside: The ten-dollar bills issued by Francophone institutions in New Orleans prominently dislayed the word "DIX" (french for "ten"); some believe that this is the origin of the terms "Dixie" and "Dixieland.")

I belong to the Irish Channel St Parick's Day Marching Club and participate in the oldest of the city's several Irish-themed parades each March. The organization was founded shortly after WWII, when veterans from the very tight community in the Irish Channel neighborhood began scattering into the suburbs to take advantage of the GI housing bill. (Those postwar loans were available only for NEW housing, presumably thanks to the construction lobby. The money could NOT be used to buy and/or renovate old buildings in old neighborhoods, which explains that postwar "white flight" to the suburbs was not entirely about racism.)

The parade was founded not only to honor Ireland and St Patrick, but also as a sort of reunion back in the old neighborhood, which over time became predominantly African-American and, later, Hispanic. The Saturday before March 17, our parade day, is sometimes jokingly called "White History Day in New Orleans."

Anyway ~ the real old-timers of the Irish Channel neighborhood were and are largely Irish, but also Italian and German. And their Irish forebearers all came to the states MANY generations ago, so there has been a lot of intermarriage with the other Catholic immigrant nationalities, and little or connection to any known relatives back in the Old Country. (Remember: the Irish quit coming to N.O. after that Basin Canal / Yellow Fever fiasco.)