Where did he "self-proclaim" that he is an online casino dispute mediation expert?

Cut the dude some slack. He is doing this out of goodwill or as a volunteer. He tries to help where he can and where he can't, he clearly says he can't. I see no reason why he should be answerable to you because he is no representative of the casino. If you want some answer, feel free to reach out stake.com's support or their in casino community/forum. A smart person would certainly do that.