Eventually it turns out the aliens communicate only by referencing historical events - their whole language is built around the concept of a shared cultural context, and understanding the emotions associated with certain past situations. In other words, their culture is only able to communicate through the use of memes; those without the shared context cannot grasp the meaning of their words.

"Shaka, when the walls fell" is a reference to a situation where two parties failed to understand one another or come to common ground.

As a bit of twice-removed meta-humor, this explanation of past events without directly saying anything about the video itself is my answer to your question.