The argument is for a 2D observer. You and I both see that the surface area of a sand grain, distributed by explosion to a different surface area with the diam

The argument is for a 2D observer. You and I both see that the surface area of a sand grain, distributed by explosion to a different surface area with the diameter of a beach ball, has a center in 3D space. But from the perspective of a Flatlander on the expanding surface, looking at the distance to an adjacent microbe, the universe is growing, and there is no meaningful point on that 2D surface from which the expansion emanates, it's expanding everywhere. There's no reason to believe our universe is not infinite. It's certainly effectively so.