They’ve also run things like the pioneer plaques past other scientists, who often have difficulty discerning the meaning behind them. If human scientists have difficulty discerning the meaning, I can only imagine what kind of difficulty aliens who speak in metaphor would have, let alone if they weren’t linguists/scientists, which appear to be the case in the episode.

We evolved to hunt, and so it is suspected that as a result of that, we understand arrows to indicate direction. A species that hasn’t evolved in such a way might not understand the meaning of arrows. Apply that same principle to language and you potentially have your problem.