The Huntsman truly was an intelligent creature. First, it lulled Atlan into a false sense of security by making sure that the arrow wasn't too fast for him to react to. This gave Atlan a chance to get used to its timing.
Atlan should have found it weird from the very beginning. After all, the Huntsman was more than capable of producing an arrow that seemed as fast as light speed. But it didn't. It only produced a speed fast enough to keep up with Atlan's slow jog.
Once he was used to the timing, the Huntsman quickly changed the arrow's objective and targeted him instead.
This was an unexpected development that forced Atlan to use all the wits he had in a fraction of a second and think up a solution to survive. Thankfully, he was able to find a way to deflect the full-powered arrow by the Huntsman.