The appearances to the disciples are both historically bound and future laden. They all involve opening the disciples up to a richer understanding of the life of Jesus and his interpretation of the scriptures. Here the mere telling of the story of what happened to them on the road to Emmaus sparks again Jesus' appearance. This resurrection thing threw people for a loop. It still does.
Nobody knows exactly what it means.
And the disciples are among the first to be clueless. It is clear from the Easter stories that Jesus was not immediately recognizable something had changed about him. Mary thinks he's the gardener until she hears him speak. The disciples traveling on the road to Emmaus do not recognize Jesus until he breaks bread. And here is this story, that Jesus appears out of nowhere to the disciples.