A isn't making two statements. The (single) statement "I am a knave, but B isn't." is a conjunction that is false because it's right hand side is false.
Still, makes me think that this could have been stated clearly instead of relying on the reader interpreting it in that manner.
Like the famous Two Guardians riddle: one always lies, the other always tells the truth, you get one question, etc. There's a translation that starts "You have a wire and a NOT gate..." in which the puzzle becomes blindingly obvious. (Details omitted so as not to spoil the puzzle for anyone.)
Once you have developed a facility with the special jargon of logic puzzles and know Prolog, I've found that, while some puzzles become boring ( https://swish.swi-prolog.org/p/Boring%20Sudoku.swinb ), many are still interesting as an art form, much like le demo scene you could imaging puzzle scene and not be too far off metaphorically.