There is no copyright claim here, the article says it's not illegal and they are right. But if MySpace decided tomorrow they wanted to finally catch up to Facebook and the result was a new site that was a near-exact replica of Facebook, naturally people would call them out on that.
1 - We are talking about an api documentation not a website used by 1B members .
2 - The person who called them out works at stripe...
3 - The design we are talking about is far from being very unique to stripe (today), except maybe for the blueprint.
If indeed paypal is copying stripe, it would have been more convincing demonstrating this through a set of new features they allegedly copied from stripe. That would have been more convincing and worth writing about.