When you are driving, or in/on any moving vessel, look at the ground close to you and compare it to the ground far in the distance.

The ground near you appears to be moving very quickly (when you are, anyhow) and the ground in the distance (or a bilboard, for instance) seems to be moving much more slowly.

The reverse of this effect is the reason you can see things moving very quickly at a great distance (of course, assuming they are big enough and light from them is received by your eye).

If the bullet were large enough (or illuminated in some way, like a tracer round for instance) you could do this test yourself to confirm - but it is the exact same situation as with the billboard.

The billboard is moving the same speed relative to you as the ground right below the window of your car, yet appears much slower. If you could fly the car up to be close to the billboard - it would appear to whiz by just like the road does (close to you) on the highway. Likewise, as you get farther and farther away from the billboard it appears to move slower and slower - even though you are still traveling the same speed.

You might want to drop this meme out of your collection.