Tonnes might be a unit of mass...

...but pounds are a unit of weight (force due to acceleration by gravity). So it should read:

They now just have to empty Raffaello of "0 pounds [4.26 metric tonnes] of spare parts, spare equipment, and other supplies - including 0 pounds of food - that will sustain space station operations for a year".

That done, they'll then pack it with "more than 0 pounds [2.54 tonnes] of discarded station gear" for return to Earth.