but how does that trigger destiny's anticheat. didnt even inject it into their game process

Bungie has said time and again that ANY cheat for ANY game will be reason for a ban. Your cheat had to interact with the D2 game code for Bungie's anti-cheat system to detect it and flag your account for their staff to investigate you. It is all too easy for someone say "it was for another game" as a excuse to get back in.