That's not what I see in that plot. I see a distribution shift, with zero linkage between before and after cases that would suggest "Half had more gray matter"

Figure 2 is the one you want https://els-jbs-prod-cdn.jbs.elsevierhealth.com/cms/attachme...

Which does show effect increasing with severity of the case. I've seen plots like that before in similar articles.

See also table 2.