It could have been a USAF fuckup. It could have been a FAC (Forward Air Controller) fuckup. It could have been an equipment malfunction.
Interestingly, a British spokesman called for suspension of judgment until the investigation is complete. He also noted that US air strikes have saved British butts in Afghanistan a great many more times than they have caused British casualties. Furthermore, he noted that the nature of the ground combat is such that totally avoiding friendly-fire accidents from air strikes is essentially impossible.
Next time, read the whole goddam article. I am in no way an apologist for my country's mistakes, but at the same time I will not accept unwarranted accusations.