He appeared in another form - In a form unlike his ordinary appearance so much so that they did not at first know him. See the notes at Luke 24:13-31. “As they walked and went into the country.” To Emmaus, Luke 24:13.
Related Commentaries of Mark 16:12
Mark 16:12
12 After that he appeared in another form unto two of them, as they walked, and went into the country.