Davis was a first-round pick of the San Diego Chargers in 2007 (he was selected just four slots ahead of Paul Posluszny, as a matter of fact), where Bills GM Buddy Nix was working as the Assistant GM at the time. The 6'1", 210-pound LSU product was released by San Diego on July 28 after four very injury-plagued seasons in which he participated in only 26 games.
Selected to be a threat out of the slot, it's possible that Nix is simply doing one of his old players a favor, as Davis has been on the open market for a week with very little action. It's also possible that the Bills are seriously interested, as Davis is a very talented player that, if healthy, would at least add to the competitive aspect of a very deep and evenly-matched receiving corps. If the team does take a flier, it will be at a very low cost with some boom factor.