Decided to look into this more. Here is a Wiki article on the reed boats of Egypt and Lake Titicaca, Bolivia:
https://en.wikipedia.org/wiki/Reed_boat
In addition, here are a lot of images of reed boats. A number also have lines as shown in the rock carving. You say bow and stern, I say front and back ends, what is the argument???
Good catch — Heyerdahl used papyrus from Lake Chad (it had gone extinct south of the Aswan Dam) and used boat weavers from the Andes to build both of his Ra Expedition craft.