its possible because he's spent literally weeks getting it ready.
as far as i know surgeoun plays loads of differant loops.
DDR plays loops integrated with his hardware set-up.
differant people do differant things.
but the basic concept is that you look at it like a multi-channel mixing desk and on each channel you can have hundreds of loops or samples loaded but you can only play one at a time (from each channel).
most would put kicks & basslines on 1, snares & claps on 2, hats on 3 etc.
(the little yellow arrows are the "clips" that are playing at the moment)
then you can bring in and out any combination of these channels that you like. while adding effects to them.
any clearer?