From their perspective, it would be management, investors, and the FAA who had the responsibility to ensure Boeing was behaving appropriately.
Financial disclosure is NOT more important than safety. Even if it involves all kinds of financial non-transparency and even financial crimes to ensure that lives are safe, at the impact of Wall Street billionaires' profits, I'm in support of it. I'd like to get to my destination alive.
If a plane can be made twice as safe, I'll buy Boeing stock at twice the price. Then when the plane is 3X as safe I'll sell it at 3X the price. Their financials don't matter to me. As a non-billionaire without a private jet, safety is how I "value" a transportation company.
Which is not to say they're even doing a good job at that, just that this particular thing isn't on them. It's not like they're being accused of cooking the books. I didn't see a charge in the article, but I would assume they're being investigated for negligence.
The story behind the lawsuit was that the Dodge brothers had just left Ford (then a private company) and they planned to use their dividends to start a competitor - which Ford suspected and which is the reason why the dividend was canceled.