But we should consider the possibility that he intended to descend to via the MR.
My gut feeling based on everything I've read is that this is the case. He was apparently a marathon runner in great shape. The report above of great weather and visibility. He could have been looking to mix it up and do a loop. He may have done some amount of research, but not enough to be aware of the true nature of that path in snow-covered conditions. Perhaps we'll learn where he fell, which would indicate a lot more about what happened, but he could have gotten partway across the traverse and decided it would be safer to complete it rather than turn back. If I look at Gaia GPS right now this is what I see (below). All discretion is left to the user to know that some of those dotted lines are very different than others.
Unless if he fell close to the sharp turn or was suffering from extreme hypoxia, I agree it's hard to imagine that anyone with even a hint of hiking experience (assuming good visibility) would be disoriented once they started making their way east down the walkoff.