The Citizens were unable to defend their Premier League title, with Liverpool winning the league.
They also failed in the UEFA Champions League, only reaching the last eight.
The Belgian midfielder told the club's official website: "A few years ago Liverpool were behind so many points and then it got closer.
"It can change so quickly and I don't think you can ever base a season on points difference.
"A lot of the time this year we played good enough, but we didn't capitalise on their mistakes and we made a few mistakes too many and the other teams got goals out of it and points.
"That's the difference. I don't think a lot has changed from the years before, but if you make too many mistakes then you lose too many points."