He is, because spontaneous is, in fact, the correct term here.

But also, mansplaining just means that someone explains something to another person when it’s painfully obvious that the other person knows everything they’re explaining, often way better than the person who’s doing the explaining. Usually requires the over confidence that comes with unreflected privilege, such as being a man who subconsciously assumes that their gender gives them intellectual authority. Being wrong isn’t a requirement for mansplaining. This would be a textbook example even if he had left out the first sentence (the part where he’s wrong).