[onewaystreet]

> I get that but I'm wondering who is this postmortem written for?

For their customers.

> In that case I don't need to basically congratulate Stripe on messing up and then posting PR piece on how they messed up, especially when it's such a trivial mistake (by that I mean it's not anything technically interesting for what went wrong).

Few screw-ups are ever that technically interesting. The point of a postmortem isn't to be interesting, it's to explain what went wrong, why, and what you are doing to prevent it from happening again in the future.