Perhaps you can see that how the DM says a thing actually puts the DM's thumb on the scale as to how the player is expected to react. I know that some are saying "Oh, but they can do what they want" on the one hand, then saying they do have an expectation that if they're not acting in the expected way, they aren't really roleplaying. At least one in this thread penalizes their XP. So I hope you'll forgive me if I don't take your word for it here.
As well, I think you may be confusing my description of the environment with the narration of the adventurer's action. If I were to say that someone is fidgety, that's going to be on the front end. It's a clue in the description of the environment that this person you're interacting with may have something going on with them. Just like the scorch mark on the wall opposite the door may suggest that there may be some danger in interacting with the door. Maybe the player picks up on this and takes action to find out more before making assumptions about what's going on and maybe they don't. After resolving, say, a Wisdom (Insight) check, then I'm narrating the success or failure of the player's action declaration e.g. "The NPC's fidgeting and stammering indicates a lack of truthfulness..." Then I loop back around to describing the environment, perhaps having the NPC continue to fidget and spin lies. What does the character do about that? Play on to find out.