If they lived in a place where the IRS cannot send them mail, why would it be hard to believe? From that very article it points out how useless the IRS contact system is:
Charles Bruce, a lawyer who advises the expatriate group American Citizens Abroad, highlighted a report from the Treasury Inspector General for Tax Administration that found that the IRS sent 855,000 notices to U.S. citizens living abroad in 2014, but the tax agency's "data systems aren't designed to accommodate the different styles of international addresses, which can cause notices to be undeliverable." The report added that "current IRS processes for addressing international mail issues are ineffective or nonexistent