As with all chemical reactions, the product(s) is/are determined by either kinetic or thermodynamic control.
Under thermodynamic control (where the transition-state activation energies are relatively low and all reactions are reversible) the products equilibrate to the lowest energy product. Under kinetic control (where the rate determining step is effectively irreversible), the difference in activation energies determines the product ratio. You might properly guess this is a kinetically-controlled reaction, since 1,2-dibromoalkanes do not spontaneously form bromonium ions and Br- in CCl4.
If you draw out the elementary steps of the reaction mechanism, following the rules for arrow-pushing (described, for example, here) you should be able to identify the step which determines the product:
The rearrangement product requires going through a non-stabilized secondary carbocation transition state (4) versus direct opening of the bromonium ion as in (1). For a deeper understanding, consider what changes to the structure or reaction conditions might favor the rearranged product.
Ref: Advanced Organic Chemistry: Part A: Structure and Mechanisms. Francis A. Carey, Richard J. Sundberg, pp. 362-371