| He's doing whats called an artificial harmonic, and then bending the string once he's made the harmonic ring out. For an artificial harmonic on bass you're fretting a note, then using your thumb to deaden the string at a specific point so that only harmonics that have a node at that point will ring out, while simultaneously plucking the string with your index finger to make the harmonic ring out. Its a simple technique once you've seen it done, but unfortunately very hard for me to explain in text. He's adding an extra twist to the technique by bending the fretted note once the harmonic is being played, therefore bending the harmonic note. He's also got a lot of overdrive and probably other effects going on, as distortion/overdrive tend to boost overtones and therefore make harmonics ring out more prominently.
My advice is to find some youtube videos on artificial harmonics on bass so that you can actually see the technique in action. Also, reading up on how harmonics work can be a little intimidating at first because there's some math/physics involved but it'll definitely improve your ability to play natural and artificial harmonics by understanding how the technique actually works.
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