What is the the big deal or confusion? ANY MasterCard is accepted payment for cashless payments on OfferUp. This one just happens to be issued by Paypal, which is technically not a bank, but can be used as a bank account.
Paypal issues 3 types of cards: Mastercard "regular" CC, a Debit Mastercard, and a Prepaid Mastercard (labeled prepaid).
The only issue MIGHT be with the prepaid version when dealing with OfferUp RETURNS, since Stripe will NOT be able to return the funds into this prepaid card, which is why there is a warning within the TOS in regards to "prepaid debit cards".