Min, I see that NW case is as yet only an accusation. Funnily enough, it reminds me hugely of an incident on one of our flights last year. Two teenage girls (who happened also to be American) made a similar accusation against a man (who happened also to be Asian) sitting next to them. It started as a timid suggestion; their mother became increasingly frenzied and by the time we landed they were near-hysterical and the police were called.
Interestingly, I haven't heard or seen anything more about it.