Stall is not speed dependent, it is only AoA dependent.
Since this is the case, you can base a "reference stall speed" on any g you like. They happen to have chosen one that is less than one.
I assume they want a "stall speed" to refer to because speed is the closest/most useful allegory to AoA in the normal Airbus cockpit.
If you really wished, you could fly an Airbus at 10kts without stalling, or conversely, stall it at 200kts.
You could also stall it whilst climbing at 5000ft/min