The purpose of the ForgottenEmailRequest is it tries to find user based on email address and if it finds the user, a password reset link is sent.
As per your post, the password is automatically getting reset, this will not happen by using the above line, it may happen only when you use any other auto reset functionality related methods in your code. Please check the code thoroughly and also the below api reference might help you understand the usage of the AuthenticationHelper class methods.
http://devnet.kentico.com/docs/11_0/api/html/T_CMS_Membership_AuthenticationHelper.htm