It's been widely reported that the three guys who are said to have started the Colby Fire were not camping in a designated campground. That's true, but one should not come to the conclusion that it was an illegal campsite. Dispersed camping -- that is, camping in a spot you find suitable outside official campgrounds -- is allowed throughout Angeles National Forest, with the exception of closed areas such as Williamson Rock (to protect an endangered frog) and the Station Fire recovery zone.
For better or worse, such a policy exemplifies one of the biggest differences between National Forests and National Parks. Generally speaking, forests are public lands where everything is allowed unless it's specifically prohibited; parks are withdrawals of public land where everything is prohibited unless it's specifically allowed.
All that said, the fire the three young men are suspected of lighting was illegal. If you want to light a fire for any reason outside a designated site in Angeles National Forest you have to get a California Campfire Permit. And unlike, say neighboring Los Padres National Forest, you cannot simply download a pre-signed permit and be off on your merry way. Angeles National Forest officials require you to show up at a ranger station and obtain the permit in person. If the suspects had done that, they would have been denied a permit along with an explanation why.
And if that had occurred, the Colby Fire may have never happened and the local media would be all about this morning's Oscar nominations announcement instead.