It doesn't say it leaks transaction history, the text says it will tell the bank if you have a long history of purchases. I presume this purchase record is to validate the authenticity of the card (if you've made a lot of purchases on the card over a period of time, it's pretty safe to say it is indeed your card). I can't see how the /contents/ of those transations are leaked via this route, or even what remote stretch of reasoning would indicate it. No bank cares what apps and music I buy, but the bank would care if I've only used it for the last 15 minutes or if I've used it for the last 5 years as a risk-calculation element.