Is "that's what" trendy usage?

When a speaker's statement is misunderstood the listener often tries to clarify it by explaining the context in his/her vocabulary. In most cases the speaker's reponse is "Yes, that's what" after he/she hears the right interpretation from the listenener. Does the sentence sound rude with "that's what" or is it a bit trendy? I would simply say "that is exactly what I tried to explain"?