You say your brother already had issues with your parents and he just moved to a new country several thousand miles away from them. His behavior already suggests a desire to limit contact; on current information, I'm not sure one could say that this is entirely the therapist's idea.

S/he may have approved of the decision, may have suggested or encouraged it, or your brother may be giving them credit for something he decided to do himself.

An ethical therapist certainly would not request that he break off communication, but as your brother is presumably an adult, it is his decision and I'm sorry to say there is not much you can do about it.

(Also, though there is a current thread about therapy and cults on here, most therapists do not belong to cults.)