It has been my experience over the years that bike collectives can be welcoming places that allow neurodiversity to flourish, but we're generally better at knowing how to identify a solution to a problem with a bicycle than the sort of problem you have described here.
There are two primary sets of skills that go into walking people through a repair. One of those skills involves knowing the mechanics of repairing a bicycle. The other skill involves knowing the processes of walking people through that repair. To use the technical terms: content knowledge and pedagogical content knowledge.
It sounds like your volunteer has the content knowledge. The pedagogy isn't coming to him so easily. Your patrons surely see this as a problem - and I think that's a key
point. This is a matter of respecting your patrons. This affects what
may well be their primary vehicle. It sounds like this can also be a
safety issue. At this time, I would not consider him fit to walk people through repairs unassisted.