First, let me remind everyone about the depth chart. Murray's backup is Dunbar, not Randle. Randle is the change of pace back. If Murray doesn't play, it is Dunbar, not Randle that will take his snaps.
Second, Williams isn't on the 53 man roster because at the end of training camp he was evaluated that he can't block and can't play ST. Maybe those things have been fixed during his time on the PS. He is a better runner than Dunbar so it is not out of the realm of possibility that he could make the 53 next year.
Third, Babe has been known to stretch the truth a time or two. I seriously doubt Williams has turned down 10 team's 53 man roster. I can see it more in reason if it were just AZ because of his bad history with them and maybe a couple of really bad teams.