Was the truck their delivery truck? If so, it is doubtful that they even worked (directly at least) for McDonald's. They would either work for a shipping company or for the food supplier that supplies McDonald's.

Unless McDonald's works different almost any other restaurant and does all that work themselves without contracting out.

This is something you should have made the manager aware of or the police.

Also there is no discrimination, on either McDonald's or even the truck driver, he (or she) was just thoughtless. I highly doubt he was actively thinking "I will park in that handicap spot so no one else can".