The line comes from Half-Life, Valve's 1998 first-person shooter, where human grunts are the military soldiers who hunt the player through Black Mesa. Their speech system gave them short, clipped radio-style responses for combat and movement, and yes was one of those brief acknowledgements. Fans later ripped and shared individual grunt lines on soundboards, where the flat delivery made them useful outside the game. It still appears in gaming edits and reaction videos because it instantly signals a weary, obedient soldier without needing any context.