It was ruled a backward pass. The player was trying to pitch it backward to a teammate on a reverse but was hit as he was releasing it, so the ball didn’t make it to the intended target. The lineman happened to be there and caught the ball and was tackled for a six yard loss. Replay could get involved to rule it forward, but 2nd and 16 was worse than the 1st and 15 for illegal touching would have been, so there’s no point in stopping the game.