First, it is intended that you did not receive a token, as you cannot get them in the rotating game modes, like One for All.
Second, it doesn't matter if you haven't gotten an S with the champion, as it is entirely possible to receive a chest for a champion without getting an S grade. This is possible by having someone in your premade party get an S grade while you were playing that champion, as the chest you get in that situation counts towards the champion that you were playing, not the one that your friend was playing.
So, I will ask you again, have you received a chest on this champion before? To be absolutely certain, you should check if you have or not by going to the champions tab on your summoner profile. If this champion's icon has a golden leafy border around it, then you have already earned a chest as them and will be unable to earn another chest as them until next season.