As a person with minimal practical experience in aeronautics, I am far from an expert. But I have no trouble believing that if a nose broke off of a large, fast-moving plane, causing the rest of the plane, traveling at 300+ MPH, to pitch up, it will head in an upward direction for a short period of time until other forces take over.
Which is exactly what the NTSB said. If you will look at the official report, around page 100 you will see some charts illustrating some computer simulations. Although all the sims don’t produce identical figures, they all show the remainder of the fuselage with wings moving in a forward and upward direction at first.
Also, if you look at the debris patterns and match what was found with the part of the plane they came from, it supports the theory that the fuselage continued roughly on course for a while.
The plane’s breakup is divided into three parts: yellow, the nose section; red, the middle where the explosion occurred; and green, the wings and remainder of the fuselage including the tail.
It seems logical that the red (middle) section, which fragmented the most and consisted mostly of tiny pieces, would begin to fall soonest. The yellow, nose section, having forward motion and inertia but no wings, would fall next. The green section had intact wings, and although they weren’t under human control, would be able to glide more than any other severed sections of the plane.
And this is exactly what was found. If you draw a line showing the intended path of the plane, you will find that the red zone is first, the yellow, second, and the green, last. So the debris field supports the overall breakup scenario.