While I get that this is a public facing post-mortem and won't be as detailed as whatever is provided internally, it doesn't sound like there's any investigation into how such failures in the future can be better contained. There should be an assumption that some bug will get through eventually, and being able to say that a small percentage of customers are impacted in the worst case rather than a global outage is a much better outcome. It also means you can export your isolation to customers to provide them the tools to manage their redundancy.
This doesn't look like a post mortem - it is a quick reaction/apology the day after and promise of a post mortem. It doesn't seem unreasonable that they need more time to dig in to the root causes.
> Broadly, this means fully leveraging the isolation capabilities of WebAssembly and Compute@Edge to build greater resiliency from the ground up.
So I guess this means it was NOT WebAssembly that caused the issue.