He was @ LSU on a track scholarship and they didn't want him playing football there, so he never played football in college. That was the reason he was a UDFA.
He's a long shot to earn a roster spot no matter what at any rate, the roster has a lot of depth at WR, and he may only be a returner. That said as you rightly observe we don't know what if anything he can do except run really fast. He may indeed have a giant learning curve to climb to learn to play WR or even as a KR as a pro or major holes in his game. You can't teach world class speed however.
He's still an interesting addition, the FO is still rolling over the rocks to find the diamonds in the rough. Throw him into the competition and let's see how he does. Given the need to protect Lockett as he recovers from his broken leg this addition makes some sense.