Logout URL performing strange

When I enter url :

http://www.example.com/wp-login.php?action=logout

it asks if you want to log out or not ?

why does it happen where I am not logged in as a admin?

If I run this url on any website like

http://www.example.com/wp-login.php?action=logout

The admin of that site comes to know that somebody logged out, when I just used this url, without admin username and password.

This happens because of a missing nonce parameter in the URL.

Every WordPress action, including login/logout, validates the nonce first, to make sure the request comes from a known source.