The problem is the REFUSAL to explain by the casino. This is NOT ACCEPTABLE under EU consumer law. It only causes bad feelings, and negative posts on the internet, which are often taken at face value.
Face value here is that a German player deposited, took no bonus, and was simply just lucky enough to win.
A player screwed out of such a large sum is going to be in a rage, and unlikely to take the moderate approach, even though this is likely to get a better result.
One thing is also missing from this story - the document request, this would almost certainly have been involved for such a large withdrawal, bonus or not.
There is nothing in the terms that dictate some game playing styles as "not allowed" when no bonus is involved.
If this is a mistake, simply shutting off the internal complaints process before it even got going is another way to ensure such issues go public. Support should have advised this player of the dispute resolution processes, such as eCogra, and Malta, that are available, not telling the player this makes them turn to the internet for help.
There is also the PAB process here, but unfortunately going public first seriously hinders the prospect of any progress, and Max is likely to refuse to deal with it, just as he as already done to another PABer who went public before the PAB could be dealt with.
Trust me, I'm a weatherman.