Young distributed a handout with a number of quotes reflecting on Barth from a number of personages with which he engaged. Here are the first two, which form a nice pair. The first is an anecdote from a Sri Lankan Tamil thinker, and the second explains what Barth was on about in this anecdote, although not addressing this episode in particular (at least as far as I know).
Daniel Thambirajah Niles, “Karl Barth—A Personal Memory,” The Journal of South East Asia Theology 11 (Autumn, 1969): 10-11.
I can recall one item of conversation in this first meeting [in Basel, 1935] which may be of some interest. Barth talked to me about our Christian communities in Asia living in the midst of men of other faith. In the course of the conversation, he said, “Other religions are just unbelief.” I remember replying with the question, “How many Hindus, Dr. Barth, have you met?” He answered, “No one.” I said, “How then do you know that Hinduism is unbelief?” He said, “A priori.” I simply shook my head and smiled.David Lochhead, The Dialogical Imperative: A Christian Reflection on Interfaith Encounter (Maryknoll, NY: Orbis Books, 1988): 34.
Barth’s judgment is not about Hinduism but about ‘Religion.’ It applies to Christianity as much as it does to Hinduism and has nothing to do with whether or not there are godly or saintly individuals who are Christians, Hindus, Muslims, or anything else. The point is not an empirical one but a theological judgment about all human activity.