ADI will not bother to lie to Manji. The arm attaching is evidence to them that he's generating supernatural fear. Understandable for what just happened with the kid, but they're not going to let him keep it because that would mean he's still purposefully feeding a patron. After what's happened with Hickey, they're not going to mess around with that.

We'd like you to make a decision on what's going to happen here, though. Would you like Manji to remain and chop off the arm himself, or would you like him to disengage from ADI? If the latter, please let us know how you intend to keep him engaged with the plot. If the former, please let us know what reasonable additional explanations would work to get Manji to cooperate. ADI can provide those!