SF - Is automatically assign contact for shared email address

Morning  Our company has contacts within an Account who share the same email address.  We have web forms integrated with SF and we are finding that a Contact is submitting a form and his name name and email address are submitted as part of the form. However, the Case is assigned to another colleague who shares that generic email address.    I thought that Contact names were only populated on a 1-2-1 match and it more than 1 contact shared the same email address then the contact name field would be blank and the user would update the field when taking ownership of the case