I am not sure that is an alb. Perhaps it is instead the falda. Doesn't the falda replace the alb for the Pope?
The Pope's falda was a type of long skirt extending beneath the hem of the alb itself. So, the alb's cuff is showing here. Think of it: The falda was so long that the Pope had train-bearers both in front and in back whenever he walked!-Donnacha