Question on SSA exempt status for retired postal worker

My father-in-law is a retired postal worker, and I am helping him with his taxes.  

 

I am not sure how to answer the SSA exempt status question.

 

Here is the information that I received online.

SSA exempt employment is not covered by the federal SSA, which means the worker did not pay Social Security taxes and is not eligible for Social Security benefits based on that employment.

Almost all employment is covered by the federal SSA.

The most common instances of pension and retirement benefits from employment that is not covered by Social Security are police and firefighter retirees, some federal retirees covered under the Civil Service Retirement System and hired prior to 1984, and a small number of other state and local