Good info. nows the discussion

Interpretation on Moral character

The N requirements states:
A person also cannot be found to be a person of good moral character if during the last five years he or she is or has been involved in prostitution or commercialized vice.

The issue here is:
whether the applicant's conduct constitutes prostitution or commercialized vice?

unlikely. prostitution is "offering sex in exhange for money". X did not engage in sex with someone in order to get money. X had a one night stand with a pretty girl who turned out to be a prostitute.

X must the certificate of disposition with his application to USCIS. If it's a violation, the moral issue may never be raised. If it's more, it will get back to the moral character. X's story (one night stand) may get him off the hook.

Disclaimer: FYI only, not a legal advice