These killers are NOT HOME GROWN.....they are foreigners that came to this country and then tries to destroy it.
Bears repeating.
I think what they mean is that the plot was developed here, without any formal outside assistance from groups such as AQ. Some of the “homegrown” plots have indeed been developed by native-born Americans, mostly black converts to Islam. I notice that they usually do seek outside (foreign) assistance, though, and in this most recent case, the plotter tried to get help from foreigners and also from a foreign terrorist organization.
That said, the headlines and the use of that word are intentionally intended to confuse. They’re intended to divert attention from the fact that all of these people, whether native or foreign born, are Muslims, and to make it sound like Columbine or some other domestic nut-case plot.