Maybe he was denying that one under his more liberal 'leeway' in the PL Referee guidelines when the ball is struck right at/deflected onto the player (which would also apply in Trent's case, as he was not much further away, if at all, and the ball did genuinely ricochet off Silva) OR because Sissoko was not making his body bigger per se, but directing other players - Riley seems to be requiring a more obvious level of intent on the part of the player handling the ball (which, tbf, I think is a reasonable, traditional view of handball)