If they're talking about traders "in Geneva", they're talking about physical traders. Can't speak for oil which we didn't trade but for ags and metals, you would take delivery since it's your business (getting stuff from A to B).
Speculation on price is not done by taking paper positions in one direction, but by limiting or increasing your paper hedge, aka trading the "basis" or margin between your physical and your paper.
The physical side requires a fair amount of "RTFC" ("caring what the harbormaster is saying") and being aware of operations.
As an example we were given in training, one of our grains trader went to inspect a ship before loading it with grain, and the local guy thought something was dodgy so he closed the doors, and shone his torch at the walls. Thousands of "stars" blinked back at them. Turns out the ship had been used recently to carry broken glass, which obviously made it highly unsuitable for grains.
But the more common stuff is e.g. overloading the ship on one side so that it leans on the side you know the controller will measure the load, or playing with the percentage admixture (basically dead beasts and dirt) to net yourself a bit more margin.