using circuit boards found inside discarded electronics
...and brand-new resistors, apparently.
It says made from discarded electronics.
Things like specific through hole resistors get discarded daily, used or not, so these can very easily all be discarded.
My first hobby supplies came from the Royal Dutch Phillips Company (that's what they were back then, just Phillips now), as they would discard stock a few months after a project ended, because stocking generals is much more expensive in the long run than just buying the exact values you need when you need them.
With a father working there it was very doable to get the contents of those garbage containers to sort into a nice mix of E24/E48/E96 resistor values, weird capacitor types, chips and more.