Its this whole debate about whether one unwise statement makes a person a racist, or is racist in itself. I don't think in this case it does. I think you need something else to make it racist.
I say that in light of all the circumstances - the aggressive behaviour of the man, his provocative remark about her only commenting on him because he was black, the fact that as a woman on the train who was by then surrounded by people staring at her (possibly because of the man's very definite attempts to make it a racist argument from the very beginning), and that she was a foreigner with limited English language skills herself.
Its also entirely possible that he did jostle her because he was the type of man to do that accidentally/deliberately - and that is shown by his aggressive response to her. Its also possible she was a particularly sensitive person. I would tend to believe that he did jostle her more than is acceptable, and her response was because he wouldn't respect her right to object to this, and nothing to do with whether he was black.
He was looking for a fight, or some kind of argument, and I bet if she hadn't been a woman sitting alone, he would have muttered something and then ignored her.