Looks pretty normal what he's doing - he's NOT keeping hold of the EHT cap, he's merely insulating himself from the floor - then charging himself up from the EHT. As such it HAS to be DC, as AC wouldn't work.
We did the same thing at school in the 60's, using a van de graff generator, and standing on a stool as an insulator - the voltage was MUCH higher of course. The voltage is so high that the students hair stands on end, and unfortunately the teacher was talking and waving his arms about and got too close - and there was a 12 inch spark from the students nose to the teachers fingers