Based on some of the things I've seen and read, I can understand why the team MAY be moving on from Cam. This offense is going to require a QB with a good degree of accuracy, which has never been Cam's strong suit. Even when you go back to games played in 2015, a career year for Cam to date, his accuracy was inconsistent at best. While mobility is certainly an asset, the QB's accuracy will be critically important in Joe Brady's offense if it's going to succeed.
New team takes on the salary, old team takes on the signing bonus.
Its one reason why I like making trades for current NFL players. You get them at a potentially discounted rate, and much of their guaranteed money is with the other team so you can move on from them whenever you want. Occasionally some guys will have some future guarantees spelled out, but the new team can address those as they come up.