How to react when professor wrongly corrects you in public?
Did you pass your thesis defense? If so, it's all water under the bridge. 

If it is eating you up inside, you could send a polite note to the senior professor (cc:ing your advisor) thanking them for the question and that now that you've had a chance to re-check things, that you are ever more certain that your method is different from the suggested prior method because of x, y, and z; but perhaps you misunderstood his question and there was another earlier method he was referring to, and if so -- could he please send the reference? (tip of the hat to @gnometorule)

If you go this route, I would frame it as a letter of thanks, appreciation, scholarly inquiry, and to keep the tone as non-accusatory as possible. As @guifa notes, some jerks professors view thesis defenses as a type of hazing -- a no-holds-barred opportunity to test your mettle; and what happens in defense should stay in defense. You do not want to drag this out. It can easily blow back in your face or the face of your advisor if the senior faculty member has a thin skin (which unfortunately many academics seem to have).

Again, if you have your Masters, then I would just be happy with that and just make rude gestures towards that senior faculty member from the safety and privacy of your own home. And don't ever do this when you become that person in a position of power.


You changed the question slightly from the initial posting from [what to do after the fact] to [what you should have done at the moment]. As note above, all questions at thesis defenses are fair -- even ones that are built on false  or falsified premises. It is, after all, a "defense" and as a scientist you should be able to defend yourself from both truthful and false/falsified statements without having to resort to ad hominem counter-attacks. You respond based on your training and experience what you believe to be correct. And obviously given that you passed the defense, the examiners thought that you gave satisfactory responses on the whole. As Queen Elsa teaches us, let it go.