That doesn't mean what you think it does. In LA the weather is almost always nice so the Sheriff department doesn't spend the extra money to get their pilots certified for instrument flying. So they have to stay grounded when the weather is bad. The pilot who was flying this commercial helicopter was instrument rated. And the helicopter he was flying was instrument rated. So in theory he could've navigated his way thru the fog. But there is a twist, the company that owned the helicopter didn't have a license to operate it while instrument flying so technically the pilot wasn't able to switch to instrument.

I have no idea if any of that mattered. It wouldn't matter to me if my life depended on it but I'm sure the pilot didn't want to lose his license by switching to instruments mid flight. Best guess is that the pilot hit the fog bank at full speed and got confused and when he tried to hang a 180 to get out of the fog he hit the hill. Had he turned in the other direction everyone would still be alive since it was just valley to that side. He would've known that since he had flown in that area for years but for some reason he went the wrong way.