Austin Collie had some pretty good years in Indianapolis with Peyton Manning. He had more than 50 catches per year from 2009-2011. Then he started getting concussions. His concussion issues are the reason that he is not on a roster right now because the talent is there.
My guess is that the Collie workout is just one of those kicking the tires type deals. He is not better than the top four or five receivers on this team right now- especially when you consider that he is not familiar with the system.