I don't see anyone running him down as he sprints by them. He's not Marquise Goodwin or Tyreek Hill fast, but more than fast enough for the NFL.
Also, contested catches are not always the product of a WR not being fast. QBs with good rapports with their WRs often throw to spots where they expect them to be and compete for the ball. Its easy to trust your WR to make a play when he's as big and tall as N'Keal.