The exception of a lawyer being a good CEO does not, in any way, prove that lawyers are not good CEOs .
The exception of a lawyer being a good CEO does not, in any way, prove that lawyers are not good CEOs .
The examples of legal signs and so on are a more specific, technical, meaning that is only used in certain contexts, such as actual legal proceedings or at least informal discussions about laws or contract terms.
When /u/flkiwi above said this phrase, they obviously meant it in the joking sense I gave, and which they had actually explained above. They agree that, in general, lawyers make bad CEOs, but they also personally know of exceptions. This is not "wrong usage", as proven by the fact that everyone who read the comment understood exactly what they meant.
This whole thing reminds me of the people who complain about the use of literally as an amplifier instead of for its primary meaning as "wrong", with seemingly no understanding of how flourishes and rhetoric work (nor even of the history of words like "very", which used to be quite similar to "literally" a long time ago).
The idea that there was some point in history were the pointer target was officially designated to be x is just false. That point in time never existed.
[All] lawyers are bad CEOs is a statement that was made. Evidence to the contrary was presented. "The exception proves the rule" was used to dismiss that evidence.
It's used in a similar way as "God works in mysterious ways".