It's not actually a breach of confidentiality if nothing identifying was mentioned or attached to the phrases/words/ideas.

If it were me, I would likely address concerns about confidentiality and ask to go over specifically what their policy is. After I was certain we had discussed to a point where I understood what my therapist says is the policy, I would then ask how that applies to the blog and online writing.
Maybe ask why they don't need my permission to use my ideas as well.

But going in, guns blazing, is likely to give you only short term satisfaction and little actual explanation for what they are doing.