Okay, I can see with those couple of road adjustments they could have taken the land’s contour and made them fit a sinister picture to give everyone a big yuk,yuk when flying over. Still not 100% sure about that intent.
That said, if the intent was to create a phallic symbol, I don't think the intent was humor.
Given the cultic nature of the island, I think the symbolism would have been for occult reasons. See my post #1836 upthread.