He was at least partially responsible for the long TD pass. Miami was in a run defense with him as the lone deep safety.
The packers put a couple of receivers right and one ran a 15 yard curl while the other went up the field. Bell went after the guy in the curl, where there already were two defenders.
The deep guy was behind Vontae and he had no help. In comes the pass and it's off to the races.
Bell should have stayed deep to help in that coverage.