What is counted
When you add a card, ShowCards records which brand it was, plus your region, language and device type, how you added it and when. That is all, and it is never tied to you or your device.
What is never sent
Your card number, card name, notes and photos never leave your device for this. There is no account, no advertising identifier, and nothing that could point back to you.
Turn it off
Open Settings, tap About and scroll to the Privacy section at the bottom. Switch off Help improve the brand list, and ShowCards stops counting and clears anything still waiting to send.