"right to work" is a very confusing propaganda name, and it is not the same thing as at will employment, which most of these states also have.
"Right to work" laws mean that an employee cannot be required to join a union or pay union dues to take a job, even if that job is covered by a collective bargaining agreement.
"At will employment" means that the duration of employment is indefinite, and each of the employee and employer may end the relationship at any time for any (non discriminatory) reason or for no reason at all.