Emma convincing herself that Scott was killed by Black Bolt makes sense. If she can convince herself, then any other telepath reading her mind will see this and know it to be true.
From a certain point of view, the murder is also true. Yes, Black Bolt did not kill Scott directly, but he certainly intended so. That, coupled with the fact he truly died of Terrigen poisoning, something the royal family could be considered responsible of, makes them quite guilty of his demise, especially in Emma's viewpoint.
It's also technically true since Black Bolt was the one who personally set off the Terrigen bombs in the first place.
Who was recording Cyclops' death and why have the Inhumans not been facing a publicity nightmare after footage of them murdering someone was made public?
How do you videotape a telepathic illusion, anyway?
Most fans agree that there was either no need for the conflict, or that the resolution could've been found in various ways. Including moving the cloud with Storm's powers, moving the cloud with Crystal's powers, using Forge's machine that can solidify the cloud without destroying it, have the mutants live off the planet temporarily while still working on how to solve the problem, etc.