where do you get its a compensatory pick?

its a real pick. if a team signs a restricted free agent, the original team first gets the right to match it (in this case), if the original teams does not decide to match the contract, then the second team gives up the pick for the upcoming draft

In the National Football League, a restricted free agent (RFA) is one with three accrued seasons (six or more regular season games with a team)[1] of service, who has received a "qualifying" offer (a salary level predetermined by the Collective Bargaining Agreement between the league and its players, known as a "tender") from his current club. He can negotiate with any club through a certain date. If the restricted free agent accepts an offer sheet from a new club, his old club has "right of first refusal," a five-day period in which it may match the offer and retain him, or choose not to match the offer, in which case it may receive one or more draft picks for the upcoming draft from the player's new club. If an offer sheet is not executed, the player's rights revert to his old club the day after negotiations must end.
quote from wikipedia