IANAL, but it's not exactly "out-of-contract." The term "payment method" appears 49 times in the User Agreement[1].
Having said that, a quick skim suggests the term is used inconsistently. Sometimes it refers to PayPal as a payment method, other times it refers to the information you enter into PayPal (ie credit card, bank account, etc) as payment methods. This is because PayPal is both a payment method itself and a wrapper service for many payment methods. For example:
Your PayPal balance, if you used your PayPal balance as the payment method or a bank account as the payment method, once the money clears the bank.
So while it is confusing, I don't think you'd get very far with the "PayPal is not a payment method" interpretation.
1: https://www.paypalobjects.com/webstatic/ua/pdf/US/en_US/ua.p...