Are you talking about the number in the heart? Or Affection? The heart icon is friendship.i do not think that member had to cheat to go beyond the stats you say is the limit...they keep going up and up well after you are givin the message the arc is finished for now if you keep performing stuff with them..with no cheating i've gotten Lin and Kali up into the 40's and beyond just by doing stuff with them
If you're able to go above the friendship limit, that's game breaking and needs to be fixed asap.