a misclassification of an employees status...exempt employee vs nonexempt employee

Particular jobs may be completely excluded from coverage under the FLSA overtime rules. There are two general types of complete exclusion. Some jobs are specifically excluded in the statute itself. For example, employees of movie theaters and many agricultural workers are not governed by the FLSA overtime rules. Another type of exclusion is for jobs which are governed by some other specific federal labor law. As a general rule, if a job is governed by some other federal labor law, the FLSA does not apply. For example, most railroad workers are governed by the Railway Labor Act, and many truck drivers are governed by the Motor Carriers Act, and not the FLSA. Many of FLSA exclusions are found in §213 of the FLSA.

Employees whose jobs are governed by the FLSA are either "exempt" or "nonexempt." Nonexempt employees are entitled to overtime pay. Exempt employees are not. Most employees covered by the FLSA are nonexempt. Some are not.

Assuming that his job is not covered by some other statute, I would say he is entitled to the retro.