How so? This is about how errors are defined, not how they're propagated through the application. Feels like you didn't actually read what was being done by the OP.
Exceptions have a hierarchical nature to them in most languages, or at least have some sort of identity to them. Your correct that the author doesn't try to change the way errors are propagated, but you can see similarities between what the author is creating themselves, and what already exists in languages with exceptions.
