Odin appeared in disguise in front of Geirroth as a guest. But since Frigg had sent a messenger to Geirroth prior to Odin arriving, advising Geirroth to not be hospitable to a certain stranger which his dogs wouldn’t attack, Geirroth ordered his dogs to attack the stranger. Because they didn’t attack Odin, who was in disguise, Geirroth decided to tie him up.