For some reason I don't feel like Apple suffered a great loss here.
BWHAHAHAHAHAHA! <sniff> Ah, you youngsters ... I needed a good laugh.
HR works for the company. Their goal is to keep the company out of legal hot water. Any other goal is secondary--solving employee problems doesn't even register.
Should he have stuck it out? Yeah, probably, but there are some bosses that are beyond unacceptable--and the boss was likely to shaft him on a review if he is that bad.
Yes, he should have talked to the contracting company before doing this. That way they would have known to steer their folks clear of that asshole boss--and they could have probably gotten his contract reassigned.
Also, not sure how it works in the US but employers owe their employees a duty of care to protect them from harm and this includes bullying and undue stress.
HR is certainly working for the company, but the whole point is that they help mediate issues to avoid litigation. In order to do this, they need to provide as much assistance to employees as possible. In fact, it's in the company's best interest for their HR department to offer as much help as possible to employees.
If a HR department just brushed off complaints, it could be catastrophic for the company if that employee took legal action.
Your view of HR is extremely narrow.
HR's job is to prevent lawsuits. That means dealing with employee problems-- the earlier the better.
One way they deal with problems is to fire people or terminate contracts. But since this guy was willing to walk out anyway, he had nothing to lose.
Let's suppose he was being sexually harassed by his boss--do you think he'd go to the agency to resolve this?