What it is
Race Engineer watches the car immediately ahead of you and the car immediately behind you, by class position, and speaks up when one of them gets a black flag, is disqualified, or is called in for mandatory repair. iRacing shows your own flags on screen, but has no on-screen indicator of what flag a specific other car is under — this fills that gap with a spoken line, so you don't have to guess why a rival suddenly slows or pits.