The customer is always right.
> They may have had slightly better luck if they'd been friendlier and not attempted to school the Discord staff on how their app should behave.
Or not. Besides, it should not matter, either they did something bad or they did not, the tone of the message may upset the recipient but when you ban someone just like that you can expect them to be upset and your first line support people should be able to take that sort of heat in stride.
Sucking up to support staff when your account has been banned for no particular reason should not be a pre-requisite for having it dealt with professionally, in fact a good first line support worker will be able to de-escalate such a situation quickly by showing some competence and making sure the user is dealt with as they should.