Wealthy whites of French and Spanish descent were also Creoles, and they did most of the dominating. Some people will blame "Yankees" for everything, but the decline of mixed race Creoles didn't come about until after Reconstruction. And considering how unrepresentative New Orleans was of the rest of the South before the 1890s, and how similar segregation was throughout the South, blaming the fall of the colored Creoles on Northerners looks like a stretch.
If you're far enough South, all problems come from the North, but for New Orleans the "North" included Mississippi, Arkansas and Baton Rouge, and the inspiration for segregation could be found in the antebellum slave codes and postbellum black codes more readily than in anything from farther North. The relevant distinction wasn't between North and South, but between Catholic New Orleans and Anglo-Saxon Protestant America. Within the South or the US, the position of people of mixed race in New Orleans was unique, but even there it was always precarious.
That's a pretty funny line.