It's about not ignoring the clear underlying cause of the bug that is screaming at everyone who reads the bug description.
Include something along the lines of "We will use the URL crate and utilize its API to avoid trivial URL construction errors like this one in the future", and I may take your postmortem seriously.
A flawless developer does not exist, and at no point did I fault any developer directly for their development work. But that doesn't mean we should ignore something that is/was clearly and inherently wrong with the code. You would think this is all stating the obvious.
So it's not "just don’t write buggy code in the first place!”. It's "this code could clearly have been written in a way that would have prevented this bug from ever taking place".
And yes, good code matters. A good language matters. A good type system matters. A good use of a good language with its type system, patterns, abstractions, ecosystem, and all it got to offer matters. This is Rust afterall. If those things don't matter, then we might as well let the code be written in Python or JS, and fully recommit to the church of TDD.