So we know that one sword was missing from the 10 in the first scene when the Heralds quit. The last Herald shows up to warn the world and Hoid happens to be there. That Dalinar got the sword which the Herald had on him when he reached the Shattered Plains. Also we know he had that same sword when he became a KR and he heard a scream of a dead spren.
So my point, which I'm sure you have figured out, is that Hoid took the Herald s sword when he first appeared and left a random shardblade instead. I forgot which powers that Honorblade gives him but with the mistborns powers as well and who knows what else this man is sick strong