Although there are some universal "pid" codes that say, ultraguage or scangauge can read there are proprietary ones that manufacturers have access to that universal readers dont.
Basically, ODBII is a universal/open format that all technicians can have access to. (per the standard)
There are things that the manufacturer keeps to themselves as well.
These "manufacturer's secrets" are only available to those willing to pay the licensing fee to know what they are and how to treat them.
(So for him to uses Chevy's "secret" pid's he has to pay the Torque app maker which pays Chevy a cut)
Basically, a pid is specific type of data. (boost, O2 bank1, O2bank2, ABS, etc)
If you know what to ask for and how to manage that data you can gain more insight to the car.