Is there any evidence that was ever really a thing / effective?
How could you possibly know?
There are plenty of examples of previously trustworthy software becoming untrustworthy, same with sites you download the code from.
That line reads like the absurd advice that security experts put out about "only download something you trust" and ignoring that nobody has a clue how to evaluate that aside form say limiting them self to FOSS and reading all the code...