I can only comment on what I have witnessed, but Sissoko's priority is to play direct into goalscoring areas with ball retention only an option if there isn't a player in such an area. Most of his attempted passes have a low likelihood of success.
Stats can certainly mislead without the contextual information. There were several games last season when Tiote racked up 50/60+ passes with a near 100% pass completion rate. The vast majority of those passes were short distance and low risk.