Capital One always emails me about double charges and weird transactions. Their fraud detection is as good or better than American Express'.
Yeah, that's pretty easy to trigger.
I'd get that when I'd buy two or three Kindle books at the same time and they'd happen to be the same price. Same with iTunes as albums are often the same price. The common factor is that with both of these services, each item is a separate transaction vs. being collected in a shopping cart.