Another question to ask is, who was the person who was abusive?
I know that a lot of - shall we say - not very employable people do involve themselves in volunteer activities. Sometimes they can actually be competent in the area in which they are assisting, but otherwise throughly socially inept. Maybe on the autistic spectrum, suffering proto-dementia issues, maybe Tourette's sydrome, subnormal IQ or EQ (I'm thinking of a number of part time helpers where I work!). Oh yes, and then there are the cross-cultural and mixed languages issues.
Am not certain if any of these things apply in your friend's case, but just saying, the volunteer team leader may be aware of something like that, and just assumed your friend also knew the background story.