It wouldn't require any training at all. It's reading motor inputs.
You're assuming that everyone's motor cortex/nervous system is wired exactly the same way. Given what we know about the variability of the human body, I wouldn't expect this to hold for the entire population.
The difference is on the level of hearing someone's chess moves dictated vs. reading their mind to understand how they perceive the game.
It is entirely a consciously composed and intentionally sent message.