Here's what I got from the Ford book:
"Upper management personnel being rotated out of their European assignments came away from the Continent impressed by a 'foreign car' called Fox. The Fox was produced by Germany's Volkswagen offshoot, Audi NSU Auto Union AG, and the line was being destributed domestically by Porsche-Audi. As Ford's (Maverick-replacement) new-car team formed, it included some of those former Ford of Europe managers, and the Fox import became the Ford team's 'unofficial' development target. Not because the Audi Fox was the car that Ford wanted to build, but because Audi's Fox had a reasonable price structure and a variety of positive characteristics that posed achievable goals."
(The Official Ford Mustang 5.0 Technical Reference and Performance Handbook)