They look similar design-wise, but both also look similar to Asana's API docs: http://developer.asana.com/documentation/ . It's just a nice way of laying out documentation.
Looking through the PayPal docs quickly, they don't show any particular similarity to Stripe, besides both being REST APIs for a payments platform.
Looking through the PayPal docs quickly, they don't show any particular similarity to Stripe, besides both being REST APIs for a payments platform.