Explain it for those of us who aren't bitcoin experts. Sure somebody can see that Air received some bitcoin but how do they know who sent it?
Think of it like this.
You've got a huge map of Bitcoin addresses on a whiteboard. You know who sent some transaction, but not all. If you can get any clues as to who's who, it helps you to deduce the rest by process of elimination. Using vanity addresses (1myNaMEisBoBhfsfdfdhjfhdfdjfh) is a clue, and hurts everyone's privacy a little.
For instance, anyone looking at the 1Air... addresses can assume these are all AirVPN addresses. That means any change that gets sent back to AirVPN customers is identified (although before, the Bitcoin payments service AirVPN required the customer email from AirVPN, so this is better)
One thing: if anyone else uses 1Air... addresses, by random chance or deliberately as AirVPN do, then that will screw with doing analysis like this. But it's better if there's no extras info to use at all, I really hope this is changed