I'd hazard that it's probably just very hard attack with the fingers. If you're not really plucking the string, but rather driving through it so it hits the fretboard, you get much more attack. Kinda like how Geddy and the Ox have such hard attack with fingers. I usually just use a pick if I have to do a section that calls for very fast pedaling or specifically a pick sort of scrape attack. When playing chords or double stops I'l usually flick my fingers through so my finger nails are hitting the strings instead, like Rasgueado in Flamenco.