They've talked about it on the radio (104.3 The Fan), and like I've said it's purely speculation.
The main idea was that Denver was locked on to Decastro. Missed that pick (and was caught off guard by Steelers taking him) and traded back in preparation for Doug Martin. Was fooled by Tampa and whiffed on Martin. While this was happening the Ravens flipped a better deal then Denver did on essentially the same move. Some say that this was Xanders making, while others say it was Elway. Elway did have the final say of course, but I think he was relying on Xanders to get things done. DMAC and Big Al (Alfred Williams of the SB teams), talked about this scenario quite a bit, and I trust Al in that he is still pretty well tied in the Broncos.