What is it called when one says "false news" but they mean "fake news" and just didn't notice the difference or didn't realize it mattered? It's like an eggcorn but the way it sounds is not quite the point here.
What you describe is a form of misspeaking.
I commend you on identifying and describing this relatively common phenomenon, but until someone comes up with a better word for it, misspeaking is probably the best word for it.
By the way, a common occurrence in this regard is when a person mispronounces someone's name, such as saying Jim Waterton instead of the correct Jim Waterston.