It seems like what happened is Chrome used a special backend for storing credit card info associated with your Google account, and this Google Payment product now literally just became the interface that let's you manage your credit card information that was already associated with your entire Google account across all Google products.
I think if there was "leakage" it happened some point earlier than this: the user thought they were storing an credit autocomplete in Chrome but actually they were storing credit card info associated generically with their Google account, and eg was already linked to Play Store for purchases. The fact that the spot where you go to manage the "Google account associated credit card info" is accounts.google.com or payments.google.com seems pretty irrelevant here.
In storing card data in product x, the assumption of the user would be that that product is storing that card data for future autofill purposes in product x
Discovering that this data has somehow been turned into an entire financial account on product y without consent should enrage any reasonable user of product x