The correct answer to this open question is the following.
Here we are talking about classical conditioning.
It is classical conditioning because the birds got used to the whistle and the clothes that looked like a referee of a College football game. So the birds associated those black and white strips of clothes and the sound of the whistle with food. So when this happened at the beginning of the football game, birds flock the field, already conditioned to be fed.
That is why the UCLA student spent his entire summer feeding birds at the Coliseum, the official home of the USC Trojans football team. He wore a black and white striped shirt to look like a referee and blew a whistle.