If Anakin can make himself look like he never fell to the Darkside as a Force ghost, I have no issues with Luke appearing to everyone looking like when they last saw him. (Or a last known image of him.) Had Rey been there, she probably would have seen him differently.
Think of it like the Salt Vampire posing as Dr. McCoy’s old flame on The Man Trap episode of Star Trek. McCoy sees his old love, looking exactly as he last saw her. Kirk sees an older woman. Soon the be drained of all salt in his body Redshirt #1 sees a hot blonde.