My impression was that Haden is slow, slow, slow. He's got good anticipation and instincts, which allows him to occasionally play faster than his speed, but when it comes down to simply sticking with a WR, he gets left in the dust. I was almost certain he was no faster than a 4.5 in the 40.
So just out of curiosity, a month ago I scoured through all the scouting reports on Haden. They all said the same thing: "fast", "good acceleration", "deep speed", "clocked in the 4.4s". I didn't see a single scouting report that questioned his speed. Which really, really made me scratch my head. So for me, at least, his 4.57 is not surprising at all.
I think he's just a guy who benefited from playing behind a very strong front-seven, and was smart enough to take full advantage of it. Not even worth it at 17, imo.