ANGLE doesn't rotate the entity. the engine has built in functions which we can't see that go through each entity every frame (probably through a linked list or something similar) and use the contents of the entity's "pan", "tilt" and "roll" to orientate the entity.

my custom physics would cycle through my PHYS_ENTS, check their quaternion "quat" or something, and use my functions to convert that to an euler angle that the engine understands and passing it to the entity's pan/tilt/roll.

julz