It's Dyneema - UHMWPE yachting cord; "the world's strongest fiber...15 times stronger than steel, yet light enough to float on water. Think it sounds too good to be true? Think again.": https://www.dyneema.com/.
That 1/16" cord has a breaking strength of 500 pounds, and it's doubled, so 1000# left me with a pretty good safety factor.

So - yeah. 225# being a conservative estimate. You... um... didn't know there were plastic fibers stronger than nylon? Ultra-high molecular weight polyethylene: very long polymer molecules to start with, and then they make it super-strong by stretching the extruded resin to align the polymer molecules. You can sometimes experience the same effect by stretching a plastic bag, and finding that it becomes stronger and resists stretching further: what was a chaotic jumble of orientations gets pulled into an organized system - all the strength on one axis.

Regarding research skills: that info was in the source thread.

Edit: so I checked, and see that you left a derogatory comment in the source thread, saying a cheater bar would be simpler. Wasn't for me - that chain-and-cord whip was already in my toolkit, so using it was an absolute cinch - and I thought it was worth mentioning the method so that people such as OP of this thread might be spared some grief. Others were drilling holes in 2x4s to bolt them to wrenches & so forth; tying some cord to a bit of chain seems easier to me.