Guitar fundamental frequency vs pitch
Pitch is psychoacoustic.  Thus, a harmonic frequency can be stronger than the fundamental, without changing the pitch heard.  This is common in some stringed instruments.  And a note's pitch frequency could even be missing from a notes frequency spectrum.  For instance: An old telephone circuit can cut off frequencies below 200 Hz, but people still have no problem recognizing a low male voice pitched at around 100 Hz.

For many timbres, humans will hear the harmonic spacing as the note pitch.  In your plot, the harmonic spacing appears to be around 130 Hz, so that will be the note pitch perceived (if played at the same sample rate at the plot axis suggest).  Not 260.