I can't fathom that even the x42s would ever consider offing a planeload of Americans to get a few of their enemies. Also, to have the drone in line and all the other technical stuff happen in a planned manner stretches believability.
I guess an awful accident caused by a few individuals screwing up their jobs makes the most sense to me.
Read the research thread and look at the radar tracks. It's really pretty easy to align things correctly for a shootdown if you have someone good firing the drone. It's astonishing how much sense this makes when you can see the radar tracks both before and after the shootdown