The rumor is they leaned towards a 3rd and Miami picking up a lot of the remaining money vs doing a 4th and eating all of the remaining money.
Philly before the trade had 3x 3rds, 2x 4th, and 2x5th so to them they have plenty of picks would rather save some cap.
Overall decent trade. Miami got a 3rd for an injury prone guy they aren't keeping and Philly there's probably a 50/50 chance that they either resign him or he leaves and they get a 4th. Worst case scenario for them is he sucks but you didn't eat much cap and still have 2x 3rds.