If you've made a complaint and aren't happy with the resolution then you can escalate. That's not to say you should, though, you should only do that if you're unhappy with the resolution and you think the professor handled the incident so badly that a different handling is needed. It's not unusual for nobody to be happy with the outcome of an incident like this.
The other student acknowledged he acted in anger. Maybe he'll reflect more carefully about ever doing it again, in which case you have a modestly positive result. But what are you hoping for, an apology? A formal warning to the student? Tarring and feathering? A complete end to American exceptionalism in any form from any person? ;-)
Depending what you want affects what options are available to do something about it. But if what you want is for the other student's wrongness to be formally acknowledged and warned/punished, then really you need to start by going to someone familiar with your own institution's disciplinary system and asking what they would expect the outcome of such a case to be.
There isn't anything in the fragment you quote to tie this aggression against you (that you are somehow ungrateful and should not speak) to the fact you're not American. If the context does tie it in (for example if the intention is in context clearly, "you should be grateful to have been allowed into the country, and immigrants should not have the right to speak in this University"), then you might have an example in which the University authorities would take an interest. They take foreign students, they probably therefore don't want them kept quiet. But the professor who's already seen the case thinks it's not that bad, so personally I wouldn't bet on it. It's "just" speech, so I expect has to meet a fairly high bar to be censured, albeit that such principles have been known in some places to be applied patchily and unfairly.
If there's a wide pattern of hostility from certain of the domestic students, against foreign students, then you aren't going to establish it from a single incident. The only productive option really is for you, other people who've experienced it, and preferably allies who don't experience it but would like it to stop, to make a sustained attempt to raise awareness that it's going on and to convince people that it's a bad thing. I'm not an experienced civil rights activist and I don't want to advise you how to conduct that campaign. It needn't necessarily be protests and banners and formal complaints. I do want to point out that as long as the narrative is, "these isolated incidents do not reflect the values of this institution" then they will continue. Only by turning the narrative into "the values of this institution are not yet adequate to address these continual incidents and should change" does anything happen.
