I'm going to go out on a limb. She was black?
I haven't read the article (and don't intend to), but I bet this "law" has been in place for years and a warning/citation is the normal method of dealing. I will also bet there was more to it than just eating a fry. I can see the picture now- Kid gets asked/told to stop doing that, kid gets belligerent (my friends are watching, I can't back down, that wouldn't be cool), escalation happens.
Or the train crew could just have been dicks.
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"In this world of sin and sorrow there is always something to be thankful for. As for me, I rejoice that I am not a Republican."
-- H. L. Mencken
Support our troops, Impeach Bush.
D. D. Richards