DY – brainwashing was not his word, it was HaKatan’s, which is why it needed to be used in context. Why not comment to HaKatan about his use of it instead? Sometimes it isn’t crucial to split hairs on the verbiage if there is a clear point being made.
It is similar, in my eyes, to that one student who pipes up during a lecture with a comment that makes everyone laugh and ruins the Rebbes opportunity to bring out a point to the class.