The operation results page is showing how many records were assigned to a group. If you had more than one of the same constituent assigned to the same group, then the operation results will count a group assignment for each duplicate record that is in the import file, whereas the Group Information Summary page will only show the amount of constituents in the group. The same constituent can not be listed in the same group multiple times, but the Group Assignment Upload will add the same constituent to a group multiple times. This accounts for the discrepancy between the two.