Because ASA and organisations of that sort have a formula. With which that percentage is multiplied to work out the exact number of people who have been affected but haven't spoken out. So thats in actual fact 13 million people.
Ooo.. 13 million out of 3.5 million viewers are affected. That must be rough

If that advert were shown to every single person in the world they would have 22,260 complaints.
Actually no they wouldn't because most of the world don't have such a high ratio of busy body old women who complain about crap like this.