I suspect what Asafa said if that he is going to the world championships with the intention of winning rather than finishing an honourabvle second or third. He’s going with a positive frame of mind.
I’m really not sure he would have made a boast of winning “for certain” when he knows his good mate Bolt is still the raging hot favourite. If I was a betting man I would still put my money on Bolt after seeing him burn the opening 100m of that 200m he ran recently