It was the first commented on, and the initial missile impact would be more than significant enough to comment on.
How do you know there was not an undetected failure mode earlier? What is your evidence?
Because I've been there and done that with things going "Ka-boom!" around me, some of them down to about one pound of Composition B (hand grenades).
Trust me, one will notice more than a pound of HE going off in contact or close proximity to one's aircraft, even if said aircraft is a 747. That event would have been commented on, most likely with some variation on the theme of "sacred fecal material."
Bump -read tonite.