Doubt the author thought of this, but I could see it being possible if its one of those SAO style VR games (full immersion) where your brain is literally connected to the game, so if you can control the character with your brain and the game can read that, then why not be able to read your thoughts, too?
The author probably was thinking that you could only read the minds of NPC and monsters. The thought of mind that some obscure user would figure out the mind-reading equipment is less than 0.1%.