People, in the heat of discussion often make unsubstantiated accusations, say things they don’t mean, or make statements that they do not really believe. But if you challenge them you force them to defend that position. And once they defend it, it is very difficult to get them to abandon that position. So when someone does make one of these outlandish statements it is often the best practice to let the statement “plop”, i.e. not respond to it. It will almost never come up again.
An exception to letting a statement plop is when an accusation or egregiously wrong statement is made in front of other people and, if left unchallenged, has the potential to cause serious consequences. Otherwise it is usually best to let it "plop". It is hard to do, it is counter intuitive, but it is amazing how well it works!