CircuitStudio does not save any user data into the cloud. All projects and libraries are stored on your local drive.
If you create or edit a library component, it must also be stored on your local drive in SchLib or PcbLib files. These can optionally be compiled into an Integrated Library IntLib file. When the PCB is updated from the schematic, during the ECO process the footprint pattern is retrieved from the local PcbLib or IntLib file.
The Altium Content Vault may be used to place pre-made components onto your schematic, directly from the cloud, and these are then stored in the schematic document. When the PCB is updated from the schematic, during the ECO process the footprint pattern is downloaded onto the PCB directly from the cloud. The footprint is stored in the PCB document.