That's the most useful note anyone has left on it. The movement rule is what everybody trips over. Knights keep travelling in the direction you send them and they resolve sideways before vertical and the text never actually says either of those out loud.
We wrote it as a rule sheet when it needed to be a first puzzle that teaches the rule. One knight and two moves and no way to fail would carry it better than any amount of instruction text.
Thanks for playing it closely enough to find that.