Ford headquarters may have had a say in it, but it's also possible that this car may have just been routinely scheduled to be built following a normal customer order and it just worked out due to production scheduling that it happened to be the 28th Millionth unit. We'll probably never know why it was that particular model. Assembly plant records would know for sure why it happened to be a Deluxe Fordor. That information might be available at the Benson Ford Research Center.
As a side note, my father worked at the Dallas Ford assembly plant from 1948 to 1969 and when he placed the order for our new 1957 Fairlane 4 door sedan, he found out several days later from the production department the day it was to be built and was able to track its progress down the assembly line. There wasn't anything special about it, just another car in the production schedule going down the line based on orders received from dealers. It was the very first "new" car he ever bought, so it was a really exciting when he stood by to take delivery right after it came off the final inspection line!