David B the pianist intentionally accentuated some notes that are not part of the obvious melody but rather isolated notes from the accompaniment, thus creating a secondary (hidden) melody. Arguably it’s not something Chopin himself intended because he would have denoted it otherwise, so the tongue in cheek title alludes to the possibility that it’s a discovery made by the pianist. I would say the truth is somewhere in between. Picking carefully chosen notes from any good chord progression would naturally sound right and resemble a melody despite not being the intent of the composer, in other words even he himself might have not “heard” it.
