Why they are positional isomers not geometrical
 

Dear Student,

They are positional isomers and not geometrical isomers because here the carbon attached to the atoms are changing. Geometrical isomers arises due to restricted rotation, however here the atoms are attached to the same carbon only. 
In the given example, the position of Br and I is changing i.e. breaking of bond is taking place. This is not the case in geometrical isomerism.