I get the paper book and credit sized card for the low season discount at campsites across Europe, and have done for many years.
ACSI more recently have introduced their digital version, which sounds like what you have.
They also used to, and I assume still do, sell a card for about £5 which did not entitle you to discounts. It was a form of ID which you could leave at a campsite instead of your passport. It had your name, address and passport number printed on it. The card also had an insurance attached to it. You and your van were insured against 3rd party risks and claims whilst on a campsite.
Davy