I didn't downvote, but your post sounds like you're implying some kind of tomfoolery, deception, or other hidden reasons. There are very likely none, it just takes time to adapt to a specific enemy, probability slowly increases while you get more attempts, and then after some time (t) the first shootdown is "properly" successful. And note how this was preceded by that half-successful shootdown where the plane made an emergency landing. And they shot down drones.

You sound like they roll an antiaircraft cannon out of the hangar and immediately successfully down a plane. That's not how that works. The AA was probably there from the beginning, just not successful.