There isn’t a difference. I am telling you from literal experience of working in US hardware assembly & then hardware assembly in Poland. Specifically Dell (computers & servers) when they moved production to Poland in 2008. Every company that has moved assembly to Poland follows the exact same practice. The ‘Made in X’ sticker is really misleading to consumers (just look at all the misconceptions in this thread) because the more accurate representation is ‘Assembled in X’. It’s sexy to consumers to have a product that says ‘Made in X’, and local governments (Poland not being an exception here) will typically require that it says ‘Made in X’ for exactly that reason. It’s a symbol of pride for that country.
Almost every part in the assembly process is already made; rarely anything gets “made” in the factory. You start with an empty chassis, you take a motherboard from a box and a line worker screws it in to the chassis. The chassis with the motherboard moves down the assembly line, and another worker installs other components on top of that. Then it goes on and on, until it reaches a testing station (that runs computer tests for passes and checks). Then there is an additional quality control check done by people who inspect for defects, loose components, misaligned elements etc.
Why Poland? Because it is a central shipping location in Europe from a view of logistics, and because they don’t have the euro currency. It comes down to cost savings across the board.