Their detailed report[0] is pretty clear, and defines what they mean for the categories they're reporting. According to that document, they had 20221 device data requests, and they provided data for 12146 of those requests (some of those requests have many individual devices). For account data, they received requests for data from 2803 accounts, and provided some data for 1333 accounts.

0: https://www.apple.com/privacy/docs/government-information-re...