Could be he had to jump for the ball, turn sideways to get the ball, juggled the ball... Could be a lot of things... Or it could be he was showboating and didn't feel like bringing it in immediately

Seriously though it happens to a lot of passes! Doesn't affect anything really. It just means the QB is either passing high/low or to the side and makes it tougher for the WR to catch it. When this happens it makes it easier for the CB to break up the pass if he's close. Not much you can do but put points into catching for the WR and Tight Spiral for the QB.