Apparently this doesn't refer to the New Orleans truck attack, since the FBI is investigating that one as an act of terrorism. Must be a different one.
They are now treating it as an act of terror but the original statement was that it was not an act of terrorism. This changed after the screenshot was taken.
EDIT: Below is a screenshot of reports at the time, before the FBI changed their tune.
Did the FBI say initially say it was not terrorism? Yes. Regardless of whether or not they changed their mind later, their initial reaction is and will always be fact. That was the point of the post.