Let's also recall that therapy isn't an equal relationship in that the therapist is there to support the client in exploring their most private matters and that disclosure in therapy is not meant to be a two way thing. The relationship is a working relationship, it's intended to give the client the space they need to explore their own issues. The therapist has said they can't give any more, i don't see how it's "extreme withholding" to not give details of why they have no more to give.

Demanding from someone something they have said they can't give is equally characteristic of abusive relationships.