Not me dismissing the other explanations, it was generally perceived as the most likely eventuality at the time- I was flying the Classic on the same route at this time. There was a nav button on the Glareshield Mode panel, which was the only selector to go from Heading Mode to Nav, and couple the autopilot to the INS Navigation system. Very, very simple mistake to make, and not be picked up if operating procedures were sloppy. Any other surmising is just that- surmising, with far less basis of likelihood than this explanation, though with so little wreckage and data recovered, no explanation can be positively ruled out. Just some are far more likely than others- in that case, I see no reason to start believing the least likely explanation.