I was surprised too, I'm guessing the white pulp is mostly water.

The only explanation may be this, unlike the green layer which I dehydrated indoors in a dehydrator, the white layer I dehydrated outdoors for this test. So unless birds got to it, my calculations should be accurate. I'm quite sure not a single piece was touched by anything when dried outdoors. I can't imagine a bird or anything eating it.

Even in a dehydrator the white pulp takes a significant amount of time longer to dehydrate compared to the green layer, even when cut to the same size lengths and widths. Meaning the cacti stores a lot more water in this layer (which makes sense). So, 2:1 doesn't surprise me.

I would however, encourage anyone to conduct their own tests to see if similar results occur.