The impression I got from the Browns forums is that they dealt Coleman because Callaway has been so amazing (although reading through camp reports, I didn't walk away with the feeling he was doing anything more than having a fine camp for a rookie).
Also, they aren't sure whether this is his 1st strike or 2nd strike in the substance abuse program because he tested positive at the combine. So this article may have been written before that occurred and just posted later.
They also seem to have a high confidence that Gordon will be back to be #2 with Callaway at #3