secondary retention strap on kydex

[grantxurismo]

Hey all,

I've been poking around for some ways to add a secondary retention strap to some of my fixed blade kydex/zytel sheaths, I've thought about some para-cord cinches or snap buttons,
After numerous hours of searching I saw this

https://www.youtube.com/watch?v=Euve3ZoieRg

Check out the sheaths @ 1:50 and 2:40

I couldn't tell if the straps were add-on accessory or just proprietary to those specific sheaths.

Thanks for the help