Dark flames came crashing down from the sky, akin to a punishment from heaven. Although the Dragon Clan Members were also in the line of fire, they didn't even try to escape.
The Dark Flames were something that every Dragon Clan Member was born with. They understood the nature of the Dark Flames better than anyone else. Unlike the other destructive powers, the Dark Flames were more controllable.
The Dark Flames could be controlled in ways that it could only harm the person that the Dragon Clan intended. And the Dragon King had absolute control over this flame. For the Dragon Clan Members, it was a certainty that the flames weren't going to harm them.
Their thoughts were further validated as the Dark Flames swallowed the entire landscape. For the Dragon Clan Members, the flame was more comfortable than harmful. They didn't feel any heat in the flame, as if the flames were nothing but an illusion.