Indeed, yes, there are definitely people who are put on PIPs because they've failed by some metric or other.

It could be the hiring process, as you rightly say, which if that's the case it isn't their fault at all, but a fault with the process.

I'd much rather an engineer be asked to move on, or just fired, if they're not up to the mark rather than having to suffer through a PIP when all the employer wants to do is to sack them,

I guess the article is trying to highlight the fact that PIPs are often used as a broad brush where it isn't improvement that's wanted, just a lower headcount.