The companies that make the software which is installed onto the kiosks / E-gates. Typically have to integrate with an existing Government border control system and follow a set of interface requirements provided by the Government.
So you may be going through the E-Gate and it perhaps refers you to the immigration officer for a number of reasons. For example, your name is similar to someone else, or they are doing a watch list check and something has been flagged to the immigration officer. That watch list check, may or may not be an issue and its just a process that they follow.
If the Kiosk or E-gate has a camera and depending where you are. It will either just take a photo that might be printed out or it load the chip from the passport and match it against the photo taken. The face matching software has to be tuned for the environment and a scoring system is used, so if its below a set limit. The traveller maybe referred to the immigration officer, this may be due to the quality of the photo taken or perhaps the quality of the photo saved on the chip.
The passport chip can also hold other data, such as fingerprints too.