Spectacular!

If you like that, maybe check out Radim Schreiber on youtube: https://www.youtube.com/watch?v=tKy2fVXCFwA.

A friend pointed me to that as she was getting interested in doing similar - and took me along on a couple of shoots.

Looking at Kordan's shots, I'd guess he's using a fast lens wide open, focused on the background, coupled with a moderately high ISO.

Schreiber claims to also use a fast lens wide open, but I find I can get closer to what he's done with, say, f/4, 30sec, low-ish ISO (800 on a D750).