If that person called them back, foreigners would have threatened him/her with all sorts of stuff such as arrest, etc.  This is the most highly publicized scam in America today, one in which Americans were actually scammed out of millions of dollars, yet no one seems to be aware of it.

IRS Scam:

The IRS does not need to sue anyone.  They also do not bother arresting people for a few thousand dollars.  They don’t send the local police or Sheriff to arrest you.  Everything they do is done either administratively or using Federal Agents.   They don’t call you up and demand immediate payment. If you are going to be arrested, they don’t call you up to warn you.  They only issue arrest warrants for people who are really bad actors and have tried to stick them for very large amounts of money, not a few hundred or thousand.  Administratively, they send you first class letters delivered by the Post Office.  Several of them.  Ignore those, and they then send certified letters that you need to sign for.  Again delivered by the Post Office.  Ignore those and they simply freeze your bank accounts and anything else you own.  If they can do that, then why would they bother with a court case that might take them years before they get in front of a judge?  The IRS does not accept payment in Itunes Cards, Amazon gift cards, or any other type of payment other than cash, check, credit or debit card (from normal everyday citizens).

Official IRS Government site detailing this scam and providing links to report it:
http://www.irs.gov/uac/Newsroom/IRS-Warns-of-Pervasive-Telephone-Scam
https://www.irs.gov/uac/Online-Scams-that-Impersonate-the-IRS
https://www.irs.gov/uac/Tax-Scams-Consumer-Alerts
https://www.irs.gov/uac/Newsroom/Phone-Scams- ... 6-Filing-Season
https://www.irs.gov/uac/Newsroom/IRS-Complete ... -Scams-for-2015
https://www.irs.gov/uac/irs-warns-taxpayers-o ... unes-gift-cards