That is a puzzler! Two thoughts:
The geese for the top section were made separately from the geese for the bottom section. When the quiltmaker realized that they came out a different length, she adjusted the quilt size to match.
The bed sat against the wall -- the right side of the quilt from looking at the pic. But they liked to have their pillows under the quilt during the day, so the quiltmaker made the top wider, so that it would approximately hand down the same amount on the side toward the room, even with the pillows underneath.