I would say whimsical, by definition, means light hearted and happy. Therefore, I think they want something less than "Baltimore Album quilt" perfect. Sounds like a fun project calling for fused, machine, satin or blanket stitch appliqué. . . Or anything else you wart to try.
I do think you're right about it being an unusual phrase to use in directions. Hey, creative quilts why not creative directions LOL.