Okay, I was not right in assuming that it'd be correct
No. I don't think the King of the Dead had something in common of bringing the woe and "your friend is now lost". If you think about Halbarad in this point, there was certainly not in any way the King of the Dead's active involvement in this. He didn't know about Halbarad's death (possibly), and therefore if he would be the narrator (since here narrator=object of guessing) of the riddle, he wouldn't say that.
I think I can divide the attempts to guess this riddle more or less to two parts: at start, most of the guesses have not yet reached the right stadium and were not ingenious yet enough to reach the right answer; later, the guesses were mostly overlarge - too much complicated, unnecessarily.