1. Why isn’t a hillul ha-Shem for an obviously frum Jew to go into a treff restaurant and sit down in the place where people eat? To any casual observer the obvious conclusion is that this a place where frum kids go to eat treff when their parents are looking.
2. Since the restaurant require those sitting down to purchase a certain minimum, and as long as the minimum is applied to everyone, why shouldn’t the restaurant remind customers of the minimum if they notice that a certain type of customer may be unware of it (i.e. a kosher customer, who is agreeing to pay the $25 minimum by merely requiresting a soda or a glass of water).
3. It would only be discrimination if they only had a minimum charge for Jews and not others, but that doesn’t seem to be the case. It seems the issue got in the news when a frum couple didn’t realize they had to pay $25 for a glass of water due to the minimum charge (probably written clearly in a menu, which, since it was all treff, they ignored).