How did the Yantra-log find out that they do not dream? Was dreaming described by someone of a different race, or are they somehow "programmed" with the concept of dreaming, in order to know that they don't do that?

Tactics focused D20 TTRPG System with Asymmetric Class Mechanics inspired by Indian Pop Culture & Mythology. · By
Hello MisterUnlikely!
It was the former. In Ananta-log, the Dwarves were the first born and were largely responsible for discovering and shepharding new beings towards civilization.
Upon meeting the Yantra-Log and realizing that they do not sleep so much as power down, discussions about dreams would have inevitably been had. Plus, so many cultures have phrases and metaphors that reference dreaming.
The Yantra-log would have quickly realized that there was a gap in their understanding and perception of the world.
They don't have to be huge stories--1000 words would be more than enough--and that would be enough to help flesh out the different races, compare and contrast. Besides, without that, much of the time, players act as just "humans in alien costumes," and while they may come from different cultures, but they otherwise seem to take up the same motivations.