Have you heard people who say they are not Christians say things which sound Christian? There is a precedent for this.
While Peter was still speaking these words, the Holy Spirit came on all who heard the message. The circumcised believers who had come with Peter were astonished that the gift of the Holy Spirit had been poured out even on Gentiles. For they heard them speaking in tongues and praising God. (Acts 10:44-46)
Recently I was talking with someone who was not a Christian. It was easy for me to assume that I could teach her a thing or two. I was wrong. I was the one needing the lesson, because as she began to share how she views the world I realized that she had a real grasp on what she needed. Even though she is not ready for Orthodoxy, she realizes her need for truth and spiritual medicine. I realized my need for humility.
Truth is pervasive. Every person has a piece of truth within them. If we pay attention, then we can see how every person was made in the image and likeness of God. That is where these Christian sayings comes from.