I think there are two distinct issues here. The first (just because one has to be first) is whether the restaurant was discriminating. It seems that it was, and that is indefensible.
But the second question is how we should react to this story, and my initial reaction is that perhaps we should take a lesson about the ethics of doing things like going to an expensive lounge and just buying water (or nothing). It doesn’t only mean this place, either. Hotels and some other establishments understand that there’s a certain gray area in which they need to cater to non-paying customers, but we should go lifnim mishuras hadin and not push it to the limit.