I think that you may both be right, While birds may flock in large numbers, I think a certain amount of CG may of be used to create the sweeping movment seem a little more fluid. Birds generally dont move in such a way.
That particular flock looked more like a insect swam, they deffinatly more like that due to the size and wight. It may of be a print base on a locust swam then the birds were superimpose on the final shot.
You can do pretty much anything with a computer and the right softwear!
I think you bofriend may of won this one!