Due to the movement of red traingular part upside and green down the rectangular area left out to be filed by yellow and green part is now 16 (8*2) sq units , instead of 15 (5 * 3) sq units originally.
if observed carefully the length of horizontal axis increases in the ratio 8:5 which is slightly higher than decrease in vertical axis (3:2).
It is a tweaked figure...........
If observed carefully........
Figure one, start from top and vertically come down 3 blocks, then move 8 blocks horizontally.....8th block is cut in half at horizontal axis by traingle boundary.
Figure two, start from top and vertically come down 3 blocks, then move 8 blocks horrizontally....8th block's horizontal axis are fully inside the triangle boundary.
Same way Check by moving two blocks vertically down from top and then 5 blocks horizontally. There is a mismatch in two fiqures
So these two figures are not exactly the same........if two figures are not exactlythe same ther can be difference in area.
Regarding the hole.
Calculate the area covered by yellow and green block in upper figure, it is 15 (5*3) sq units
Calculate the asame area covered in lower figure, it is 16 (8*2) sq units.
So there is one hole of 1 Sq units.