He manages to achieve fast keyboard playing and good responsiveness with the LEDs.
No he can not physically do that. We have many people here who try that and they always drop MIDI messages.
What makes you think that is controlled with an Arduino using WS2812 LEDs? Certainly the "sparks" off it are not created with WS2812s.
inside info says he is using a custom arduino build running from the tutorial I posted.
What inside info?