From the article:
At the top, Boratenski found nylon cords as well as a metal carabiner. He used the nylon instead of the metal as an anchor, something he now knows was a terrible mistake.
I thought this was something all beginning climbers learned, but maybe it should be reiterated. Never run nylon against nylon as an anchor. The friction of the rope running through the sling or cord will create heat which will cause failure.
If there are no rap rings available, then just leave your own biner. For about six dollars, it’s worth your life.