Can someone explain to me how we lost this kid? Did we get anything for him?

According to the PalmBeachPost, http://www.palmbeachpost.com/sports/...0dolphins.html

the Dolphins have "acquired" the Chiefs' 2nd leading tackler on special teams, OLB Erik Walden. For a team who is depleted on defense and pretty poor on special teams, how or why did we lose this guy?