Those are what I term "boiler-plate", basically covering their behinds for all circumstances.
First, you have to remember that formaldehyde is present in all wood, trees cannot grow without it. So when Masonite states, "free of formaldehyde" they are incorrect, what they should say is "no added formaldehyde". There is formaldehyde in their product, but they didn't add any in the process of manufacturing it.
Wood dust has been considered "harmful" for many years, so they are telling you that if you don't use dust control, you can be exposed to "harmful" wood dust.
I assume that their legal department said "we have to cover every possible contingency" (just like there is something like 10 warning labels on every step ladder) so if someone claims injury by using their product they can say, "we told you about that", no matter how obvious (or not) the danger was.
When I order NAUF (no added urea formaldehyde) materials, all I worry about is whether formaldehyde is used in the manufacture of the product. I know there is formaldehyde in it, and I know if I cut it on a saw, it will generate dust which is considered harmful. Those two things are inherent with all wood products. All I care about is whether the manufacturer added formaldehyde during the process of making the board, that's all I can control.