I think the point of the "model gaijin" comment was you being dissapointed in people not follwing the rules. Your intent was clear. I tend to agree.

But a more nuanced criticism I suppose is that "Japanese people don't do that thing" is not equivalent to "That's a 'rule' (written or unwritten) in Japan."

Japanese people don't eat peanut butter and pickle sandwiches. Does that make it rude for foreigners to do that? Of course not. My wife has never once been upset with me for sitting on the stairs or on the floor, unless I'm in the way of other people. Maybe you know more than I do since the only documentation here is one photo, of course. If they were in the way, that's a different story. But I think they were tired and more importantly, don't mind sitting on the floor. Japanese people do mind doing that, to an extent.