If the message was as compact and low level as possible it was probably a bit flag, so in that context it makes sense to repurpose it.

Being so removed from binary and bit level interactions it can be easy to forget things like this.

I agree with the GP; I don't think code reviews or testing was the problem.

I think the best-practices they violated is that they deprecated and repurposed a flag within a single release cycle. That sort of activity should take two release cycles at least, one to remove the old functionality and one to add the new functionality.