First off, is this the only peach you have with these symptoms? I have researched peach diseases and not found anything that resembles the picture of the peach you provided. From what I can see, the leaves look unaffected. My guess is that the peach has an unexplained growth with no identifiable cause. Sometimes, unknown malformities occur in nature with no explanation. There may be an insect that has burrowed into the peach causing the strange looking growth. You may want to keep watch to see what changes occur and possibly give insight to as to the reason for the unusual bump.