The parent poster is correct. This is a standard practice for polygraph interviews. The pick one question, more or less at random, and double/triple/quadruple down on it until you break. Or don't.

I got "have you ever committed a crime" (and after a actually pretty cool conversation about filesharing vs recording songs off the radio with a tape recorder, I passed). A friend of mine got "have you ever had sex with animals." I don't think he enjoyed his experience quite as much.

Technically, nobody can know for sure, even someone who was there cannot read minds. But I posit that it’s way more likely that it’s part of the standard intimidation technique used by basically every professional intimidator ever – i.e. pretend to be angry and convinced about the person’s guilt in order to get them to either confess or to break down.