You cannot initialize an ActivityCategoryToken directly. Instead, you must utilize the FamilyActivityPicker and obtain your category tokens via a FamilyActivitySelection.
The example you provided is misleading for several reasons:
The ellipsis "..." likely implies that the developer needs to figure out the implementation. However, this approach is problematic since it's not feasible to generate an ActivityCategoryToken from scratch. One must either retrieve it through a FamilyActivitySelection or decode it from a Data object.
There's no method to determine if the ActivityCategoryToken instance you are dealing with belongs to the "Social" category. The only workaround would involve prompting the user to select the "Social" category in the FamilyActivityPicker and... trust him or her to do so.