A myth is a rumour turned into a legend.This then is the principal difference between a rumour and a legend. A legedn gets better -- and a rumour worse -- with each re-telling. This applies as much to legends and rumours of a race as to those in the life of an individual. Never look down upon a rumour; it may yet be lifted to the level of a legend, depending on whom it is about, and who handles it.
Or look at this way. A person with a divine presence may be a legend; the devotion of a beholder may be a rumour which his rivals will promote. And yet, respect the rumour; it has a way of turning into a legend, or even into history.