I don't think visibility is the issue here. IMO this expert's testimony is more intended to going towards showing the reasons why a disabled person might feel more vulnerable and consequently the whys for their reactions, if they find themselves in a situation of perceived danger, confrontation, etc.
This could, and I AM NOT SAYING IT WILL, count towards the "reasonable person" criteria Masipa uses if coming to a culpable homicide verdict, since although, as Prof. Grant notes in a couple of his posts, SA law has to date been reluctant to take into account disability as a part of the "reasonable person" criteria, in most modern democratic countries including the UK as the witness has referred to, this is changing as disability rights and promoting the understanding of disability becomes ever more prominent.
JMOSNNFS,I,OR