Former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE stood his ground Friday in defending a testy exchange he had with an Iowa man at town hall earlier in the week.

In an interview with NPR "Morning Edition" host Rachel Martin on his campaign bus Friday, Biden defended his comments, saying, "The fact of the matter is this guy stood up and he was, in fact, lying."

"And I just pointed out, you're a liar," the former Delaware senator continued. "It's a fact. He lied, period. And so, you know, maybe I shouldn't have kidded with him about that."

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During the exchange, the man made debunked claims that the former vice president sent his son to work for an energy company in Ukraine. The Iowan also challenged Biden about his age, which prompted Biden to challenge the man to a series of tests, including a push-up contest.

Biden told Martin that he was joking.

"He said, 'You're too old. I can't vote for somebody as old as you,'" Biden recalled. "I said, 'OK!' And he was challenging me what kind of shape, and so I kidded. I said, 'Want to do a push-up contest?' I was joking."

Biden's interaction with the man came across as off-putting and uncivil to some voters, according to the radio station, but Biden stood firm, saying that there was no intended malice.

"That's not civil?" Biden said. "To call someone who lied a liar?"