I mean it's not an in-game level creator, but yeah we kinda did make a piano roll. As Toad said the pitch of the notes is based on their y-coordinate in the editor. All the non-drum sounds are just a single sample being pitch shifted by 1 semitone every 8 pixels. Definitely the thing I'm most proud of as the programmer for this game, and it saved me a TON of time when copying the level into the game from GrageBand since I didn't have to manually set the pitch of each note 😅