Bungie's engine is unique in that it's form of hitscan still sends an actual projectile in-engine, it just completes it's travel within one frame. Like, the flight and everything is still calculated, it's just functionally hitscan.
This is different from earlier and other engines where hitscan was calculated client side or some other calculation but bullet shot was entirely cosmetic.
Allows neat stuff like the thorn projectile to actually get stuck or deflect and for bullets to have physical impacts and sound effects when they go past something.
But that's really picking at technical trivia, as much as the general playerbase cares it's the same hitscan from other games. But that was what the DMR and Pistol were in Reach.