The first part of the ID contains a unique manufacturer ID. Companies do not have to be MIPI Alliance members to be assigned a unique manufacturer ID.
The second part of the ID normally contains a part number (which is normally divided up into general and specific part info for that vendor), as well as possibly an instance number which allows for multiple instances of the same device on the same bus. The instance ID is usually fed from a pin-strap, or fuse(s), or non-volatile memory (NVM).
A random number may be used for the part number, although normally only for test mode, as set by the Master using the ENTTM (Enter Test Mode) CCC. When a device that supports random values enters the test mode, the PID[31:0] bits are randomized. When the Master exits the test mode, the devices reset bits PID[31:0] to their default value. The use of a random number allows for many instances of the same device to be attached to a gang programmer/tester, relying on the random number to uniquely give each a dynamic address.