The Google study emphasizes what Google tests for, not what you need for the profession. If you start your own software company, for example, is the Google material critically important?
While it's applicability to actual software development is debatable, the Google interview is not substantially different from other top tech company interviews.
I'm sure the author will be well-served with this knowledge even if they don't end up working at Google. There are dozens of other companies which will test the same knowledge (and also pay well).
The IB comparison is apt. People routinely study extensively and run a gauntlet to get a job at an investment bank, and that preparation is generally applicable to multiple different banks.
True, but both of those are professions. Qualifications that you carry irrespective of your employer. Being 'a Google engineer' is not the same thing, although people might like to imagine it is.
If he doesn't get the job, he's still got the knowledge. And 8 months is nothing compared to multiple years in college.