They really played on the perceived "universal truth" that CFA has the best chicken sandwich ever made in the history of ever. It seems to have paid off mightily. And, again, I do love me some CFA, but it doesn't shock me that, with a little effort, another chain could rival them.
Controversial opinion (now, apparantly): CFA spicy chicken sandwich still the goat. No sauce needed. Couple that with the waffle fries and, well, back to the drawing board Popeye's.