You do have "Wait for pending payments..." checked in your Seller Admin > Payment Preferences, so we should only have logged the order and issued a download link if Google Checkout notified our system that the buyer's payment was good and completed.
You are also redirecting to a Common Thank-you Page URL where you are advising buyers to watch their email for download details. Buyers would be directed to that page after finishing checkout successfully regardless of their final payment status, and we would only send them a thank-you email with a link to the download page once we received final confirmation of Completed payment.
It's possible the buyer used a stolen credit card that was reported after they'd already paid, but I'm not seeing any orders with a Reversed payment status in your E-junkie Transaction Log, as would happen if Google voided the payment after the fact. I'm wondering if perhaps Google misinformed you re: the "declined" payment, but we can investigate further if you could email our Support team the relevant Transaction ID: