The comet does not change but its position in the sky does btw. Longer exposure times turn points into streaks if the object is not tracked to compensate for this.
Yes, I assumed tracking as it's basically a mandatory requirement when you do telephoto astrophotography, and definitely used in the OP photo. The alternative is to shoot wider angle and align the images during stacking, but either way you have to get your subject's pixels aligned or the result is just blur.