It seems more likely to me that ARIN is following the text of published policy, but Capital One found a way to interpret it that violates its spirit. My guess is that they're treating each customer debit/credit card as a serving site that qualifies for a /48. To address this, ARIN should fix the policy, not raise fees.
It's ARIN's job to call BS on BS justifications, otherwise they're not following the policy, they're following whatever they allow. "The purpose of a system is what the system does" and all.
That's an interesting idea for how they justified it. There might be something like 4 billion active credit/debit cards in the US (but they probably weren't all issued by Capital One).
For better or worse, you're not; that's for IPv4 /16. For IPv6 /16, it'd be the X-Large service category, so $16,000/year.