To assume that the absence of a memory is evidence that the event referred to by one (who claims to remember that event) is evidence that the event did not occur is a bit like the “logic” expressed by the atheistic reference to God.
In reference to the popular notion of an all-powerful, invisible God, this individual claims that the absence of evidence is evidence. Since there is no evidence that God exists then God does not exist.
And, since there is no evidence that what person B remembers about an event in person A’s LIFE did in fact happen, then that event did not happen.
The Atheist and the Denier appear to have much in common.
Their claims are very Narcissistic.
Note: we are all narcissistic; some more or less than others.