I think that's the media emphasis. They aren't saying they have no clue exactly. DOD says it ain't anything of their's missile or otherwise. NORAD says it ain't anyone else's missile or any threat of any kind.
DOD says not a missile of theirs, NORAD said not anyone else's missile either. The headline could as well read: "Government says no missile, no attack, no threat."
That leaves a lot of jet contrails to have "no clue" which one it is.
All the various agency statements have done nothing but feed into the media's sensationalism and the public curiosity. It was 18 hours before anyone even referred to it as a contrail. If it's such an obvious possibility, it's hard to believe so many people could go so long without floating the theory to assuage the growing public concern. Honestly, they floated a “rocket enthusiast” theory (which is almost as unnerving as the hostile sub theory) before they got around to this one. They were clearly scrambling for an explanation and throwing sh*t against the wall in the early going. How did something so obvious and logical elude them for so long?
That aside, I've seen many contrails in many forms (including your pictures) and more than a few missile launches out of Vandy. I never mistook one for the other. But that's just me.