In the parable of the sower, Jesus talked about seed that fell along the wayside, and the birds came and ate it. He went on to explain, “When anyone hears the word of the kingdom, and does not understand it, then the wicked one comes and snatches away what was sown in his heart. This is he who received seed by the wayside” Matthew 13:19
So we just have to wait and see who the real believers are because sometimes a person will make a profession of faith, will fall away, and then return. That is a prodigal.
The difference between a prodigal and someone who is not really converted,, is someone that has professed faith in Christ but walks away and never comes back, then they are like the seed that was sown along the wayside, however, a prodigal will always come home.