First, I've been in the loop on a fair number of incident investigations - none involving aircraft. But given my role as a pressure equipment engineer (airline fuselages are, among other things, pressure vessels), I've seen enough jumps to false (even impossible) conclusions written up to know that most folks' "common sense" is not always properly applied, and news reporters are no experts either. So wait until the NTSB report comes out for authoritative conclusions.

On a related note, I'll point out something related to fatigue failure in metals. I work mostly with steel and steel alloys, not aluminum. I'll defer to an aluminum expert if one shows up. Fatigue is a result of cyclic tensile stresses. Determine the three dimensional state of stress to start with. Most engineers will default to simplifying that to a von Mises stress. That's fine for most cases, but for fatigue, you need the first principal stress after you've figured out all three principal stresses. Then you have to look at the difference from the maximum P1 stress in a cycle to the minimum. Have I bored you yet? But all of that evaluation leads to... an idea of where I'd expect a fatigue failure to occur. Such a failure would exhibit itself as a crack initiating and propagating until a tensile (tearing apart) failure becomes apparent. The crack surface will have "beach marks" readily apparent when looked at with a microscope with modest magnification. I'll leave further details to metallurgists. Let me know if any such indicators are found...

Note that I said "tearing" above. That's a completely different failure mode to "buckling". Buckling is caused by local or global structural instability. It is only possible with high absolute value third principal (P3) stresses. Buckling is a function of stiffness, not strength as tensile stresses are. The fuselage can be simplified as a simply supported beam, with the nose landing gear as one support and the main landing gear as the other. Fundamental structural / mechanical statics here. With a load (weight) on such a beam, the beam will bend concave up. By definition, the top of the beam will be in compression, while the bottom will be in tension. Still reading, still following?

Ok so the fuselage in question suffered a significant structural overload. One side - the bottom - was in tension. It didn't exhibit failure that we know of; I've not seen that the bottom of the fuselage tore open. Some version of inspection / non-destructive examination would be required to find small (for now) cracks if any exist. The other side - the top - was in compression. It exhibited wrinkling. A failure mode caused by compressive loads. Not a failure mode commonly associated with fatigue. I'd be hugely surprised if the buckling failure evident in the top of the fuselage had any relationship to cyclic loads.

But as I said... I design and evaluate pressurized cylinders and know nothing about aircraft. I'll leave conclusion drawing to the NTSB and Boeing engineers who have a better understanding of the art than I do.