has_one and has_many in same model. How does rails track them?

I a little confused about how this work even if it works properly. I have a model that has two association to the same other model.

Company has an owner and company has many employees of the class users.

here is my company model:

class Company < ActiveRecord::Base
  validates_presence_of :name

  has_many :employee, :class_name => 'User'
  has_one :owner, :class_name => 'User'
  accepts_nested_attributes_for :owner, :allow_destroy => true
end

here is my user model:

class User < ActiveRecord::Base
  include Clearance::User
  attr_accessible :lastname, :firstname #other attr are whitelisted in clearance gem
  validates_presence_of :lastname, :firstname
  belongs_to :company
end

Now assuming I have 3 employee of this company including the owner. When I first create the company I set the owner to the employee with id 1 and the two others (2,3) are added to the employee list by setting their company_id (user.company=company). All three have their company_id set to the company id which we can assume is 1

when I ask for company.owner, I get the right user and when I do company.employee, I get all three.

If I change the owner to user 2, it removes user 1 from the employees automatically by setting it's company_id to nil. This is fine and if I add him back as a simple employee all is still good.

How the heck does rails know which is which? What I mean is how does it know that an employee is owner and not just an employee? Nothing in the schema defines this.

I have a feeling I should reverse the owner association and make company belong_to a user.