As mentioned, it was a bent harmonic. Did you see how he grabbed the top of the guitar body and the end of the neck? He was holding the guitar and bending the neck forward to loosen the strings slightly, which lowered the pitch a hair. When he let go, the neck bent back and re-tightened the strings.
Right? That big E string is tuned VERY low....But that's my only problem with guys from Candyrat, all those out tunings. Sorry, I don't have $3000 to spend on strings every month :/