Here is a photo of a seedling of mine, that is doing a similar type of pleating. because the pleating is not as extreme, you may be able to understand it a bit better. It has Hanson lines on one side, and All American Chief on the other.
See how the petals curl back on themselves so far that the top of the petal is actually visible under the petal? You can stick your finger in there, as it forms a tube.
