What you should care is a behavior. You should be open about what is expected. People change behavior all the time depending on the situation/group/company/context.
This is a false assumption. Especially generalizing the behavior in such an adversarial setup as a job interview to a regular day to day work/life.
> Telling people how I would want a good candidate to behave during an interview
You should tell them the rules of the game. The thing is, with interviews, there are already predefined assumptions, such as not knowing something takes a point from you, so people avoid this. In your case, you are altering these assumptions without disclosing it. So people might already had changed their behavior for the interview specifically - avoiding admitting not knowing something.