The middle row of squares are slightly smaller, so even though you have the same number of squares and it looks the same, the amount taken from that row equals one square.
The large chunks were cut on the diagonal. So when he rearranged them, maybe the squares weren't perfect squares any more, and he was adding or subtracting from the total area?
The large chunks were cut on the diagonal. So when he rearranged them, maybe the squares weren't perfect squares any more, and he was adding or subtracting from the total area?
That's part of it, the squares have markings for him to line them up to shrink the sizes to make the whole thing smaller, but the same number of squares to fit in the box, but the whole of the thing is a different size with same number of squares.