@laiseran first of all, i would've appreciate if you mentioned that the earlier chapter was Love Love Deluxe part 4 where you got the explanation.
second of all, i reread the info pages from LLD part 4 and from chapter 99.
the chapter 99 is the legit one because its presented from a narrative stand-point, the same way the Wall Eyes were described the first time.
the info pages of LLD part 4 just sounds like some research study that someone from Morioh did (the "Probably" and "For some reason" doesn't make the info sound too credible).
what's odd is that the UJ release of that chapter doesn't have that line about Rock Humans not being able biologically to reproduce with Humans.
It only got added in the volume version.
I don't know why.