That one video didn't show the shuttle sideways, as many assumed, it showed the shape of the camera aperture during an out-of-focus period. Your other points are good, though.
It may be an optical illusion, or a trick of the camera in seeing an apparent yawing movement perpendicular to the line of flight, I don't know. But that coupled with the initial speculation (just that) of a control system problem makes me think he got out of alignment in yaw, then went into a spin. Once the less-protected portions of the fuselage were exposed to the friction, it'd be done for. They did see that thermal anomoly along the one side. Again, does that reflect the root cause or a further symptom of an earlier problem...?