Fallacy of Irrelevant Thesis _ involves proving a valid point, but not the point at issue.
A type of “red herring” fallacy (Ignoratio elenchi) “ignorance of refutation”.
Example taken from Dr Jason Lisle’s book “Discerning Truth”:
Suppose I was the sole survivor of an airplane crash. When a reporter asks me how it was that I was able to survive, it would be fallacious for me to reply, “Because if I hadn’t survived, I would not be here to answer your question.” Although it is true that I would not be around to answer the question had I died, this really doesn’t answer the question itself-why I was able to survive. All fallacies of irrelevant thesis can be rebutted with this simple phrase: “True perhaps, but irrelevant.” -Dr. Jason Lisle, Discerning Truth p. 81