The 30% discount is for all Annual Passholders who had valid passports as of March 14, 2020 (when Disneyland Park and Disney California Adventure Park closed). The official Disneyland website reads:
We are excited to share a special merchandise discount for our Disneyland Resort Annual Passholders! Passholders who held active Passports as of March 14, 2020, the park closure date, can receive 30% off select merchandise purchases at Disney owned-and-operated locations at Downtown Disney District and Buena Vista Street. This offer is valid Monday through Thursday, beginning January 18 through February 25, 2021.
This discount can only be used on weekdays at Disney-owned locations and is not valid on previous purchases. Further details can be found here.