No, it is NOT required that you earn PDUs in multiple categories. So theoretically, you could earn all 60 PDUs as Category A PDUs. That is not a problem.
However, PMI has recently introduced The Talent Triangle. This triangle goes into effect in December of this year. Once it is in effect we PMPs are going have to start earning PDUs that meet the new Talent Triangle components of Technical Project Management, Leadership as well as Business and Strategic Management.
You can still earn all your 60 PDUs in Category A, but at least 8 of these PDUs have to be earned in each these three broad topics. (So 8 in technical, 8 in leadership and 8 in business.)