It's pretty clear from the original thread and the reply that the implication is that Postmates was the first to offer subscriptions through iOS without going through IAP, therefore bypassing Apple's 30% cut, not that they "invented subscriptions."
"no one has ever done it" - it definitely sounded to me like they implied to transform something that used to be a "pay per consumption" into a "service". Which is definitely untrue, Creative Cloud preceded them by half a decade, Amazon Prime was before that, and arguably Netflix inspired everyone.
