Yes the cart slides into the heavy hitch receiver and the weight is carried by the cart's cross bar which is directly under the hitch 3x3 tube. Its a pretty close fit, so close that I wanted to put some of that 1/16th inch rubber over the cart weight bar to protect it, but even that was too thick so less than 1/16 inch gap, under weight it flexes a bit and rests on the cart weight bar.
Now lets say you have a quick hitch on your tractor like the Land Pride QH10 I purchased, and you want to install the heavy hitch and weights. You roll the cart out to the tractor, pick the whole thing up off the ground cart, hitch, weights with the quick hitch and tractor 3pt, then just unpin the cart from the heavy hitch and pull it off it doesn't weigh that much. To remove the heavy hitch with weights from the tractor and put it back on the cart, just raise it up, slide the cart onto the heavy hitch receiver and lower to the ground and roll away. That's how it works.
To be clear there is no weight on the cart when you install or remove it, the tractor 3pt has the hitch and weights lifted in the air. You lift the cart into the air and slide it in/out of the hitch receiver. The "flex" so the hitch and weights rest on the cart cross bar really is the wiggle room in the receiver its not that tight of a fit.