An acquaintance made two statements about the same event. The statements are incompatible. One is probably true. But it’s impossible that both are true. Only question is which statement is the lie and which the truth, and that’s not answerable.
But no, this is not some version of that conundrum in which you have to figure out how to act on a statement made by someone from a tribe of liars and you might get eaten by alligators or something if you don’t guess right.
In this case I don’t much care which statement is true and which false. The specific matter is minor. Nothing is at stake. No alligators are involved. My rambling brain is just piqued by the nature of the lie, which would be very different, depending on which statement is false and which true.