They say it's "anonymous" here, but combined with the "unique device identifier" they already said they collect with it, you have to wonder exactly what "anonymous" means in Apple-speak.
They mean anonymous as in it isn't directly tied to your name. It's possible that is has how much you spend, what apps and websites you use, what areas you live, spend your day, shop and eat, where you go at christmas, how often you go to the hospital or what day you go grocery shopping, how fast you drive and how far each week.
They can collect an incredibly dense picture of your life, but as long as they refer to you as 155264 rather then your real name (which isn't really that useful to marketers, as any sane person would freak when they saw their name in banner ads on a website), then they can say it's anonymous