It did need the needle threaded, as there were 1-2 defenders close to the flight path of the ball. Despite what you probably want to think, Purdy has shown multiple times he can do. He didn't that time, he threw off his back foot (a tendency of his)
It certainly wasn't an easy throw to make, but one that he has made before several times.
Yeah, live he looked wide open but in real time the ball had to be placed and thrown with velocity. It wasn't anything close to a routine throw.