Good to know that about the american culture as at the moment I was a little bit puzzled about the behavior. That probably also because while indeed I have invited the student in the city, myself being so without too much money and considering the discrepancies from the 2 worlds we are living in...I thought that he would be more sharing and splitting the costs. But, at least from cultural point of view, it makes sense...and I might look at that experience through different eyes now.