"Guaranteed" money does not mean "if" they make the team. If you cut the player, you still have to pay him regardless. If the player gets injured, you still have to pay him. The only way you wouldn't have to pay a player "guaranteed" money is if he is suspended by the team or the league, and the NFLPA doesn't step in (like Terrel Owens in Philly). A $14 million roster bonus cannot be part of the guaranteed money, and that would make Bell's contract larger than the $20mil/4 year deal he signed. Its just a bonus, like another incentive in a contract.
I saw the Bleacher Report article, and it cites a source from CBS, but I believe that source made a typo or was just misinformed.