I was in the room when Warren Buffett gave a surprise interview at Berkshire's annual conference. The mood swung from excited to gloomy, then hopeful.

• I was in the room when Warren Buffett unexpectedly sat for an interview on Saturday.
• He warned of a "gambling mood" in markets during Berkshire Hathaway's annual meeting.
• The legendary investor also underscored the threat posed by nuclear weapons and deepfakes.

I was in the room when Warren Buffett sounded the alarm on "gambling" in markets, nuclear weapons, and deepfakes on Saturday.

During Berkshire Hathaway's annual shareholder meeting, the company's chairman and former CEO joined CNBC's Becky Quick backstage for a surprise interview.

The pair's conversation was broadcast live to the crowd of thousands seated in the CHI Health Center in Buffett's hometown of Omaha.

I had a bird's-eye view of the event from the press box overlooking the stage, and could see the crowd's excitement at the prospect of hearing the business icon speak.

Buffett, a renowned bargain hunter, has struggled to find deals on stocks and businesses in recent years. He told Quick that today's market is "not an ideal environment" for deploying cash.

The benchmark US stock index, the S&P 500, has surged by 27% over the past five years to record highs of above 7,200 points. Berkshire shares have slumped by 8% over the same period.

Berkshire sold a net $8 billion worth of stocks last quarter, fueling an increase in its cash pile to a record $380 billion at the end of March.

Addressing the challenging market and Berkshire's ballooning cash reserves, Buffett said the company has the right people and is set up to "pick our spots."

The business icon put his legendary patience into sharp relief when he said that out of the past 60 years, only "five of them have really been juicy."

Buffett, 95, is known to invest only within his "circle of competence." He told Quick that he has not learned about any new industries in the past decade, and doesn't plan to change that.

'Gambling mood'

Buffett described the market as a "church with a casino attached," referring to the divide between speculators and long-term investors focused on company fundamentals.

"The casino's gotten very attractive to people," he said, nodding to the boom in short-term trading and more aggressive use of leverage in recent years.

"If you're buying one-day options, or selling them, that's not investing, that's not speculating, it's gambling," Buffett said.

"We've never had people in a more gambling mood than now."

Buffett couldn't resist taking a shot at the "wonderful trading departments" that practically shut down during crises.

"Just try them out when the market is collapsing," he said, adding that if they do pick up the phone, they'll use any information you give them to "go out and kill you some other way."

"It's really like going to a slaughterhouse," Buffett said. "You don't feel like eating hot dogs for a while."

From worry to hope

The mood in the arena turned dour as Buffett described the threat posed by countries with nuclear bombs and the risk that something could "fall out of the sky" at any moment.

The investor said it was important to be aware of that danger, but added that it does "no good to worry about it."

Buffett restored the room's good vibes when he joked about his lack of travel in recent years. When Quick asked if he had met the new managers of some of Berkshire's key holdings, he sent ripples of laughter through the audience by quipping: "I haven't met the old managers."

The former Berkshire CEO, who made way for Greg Abel at the start of this year, also sparked chuckles in the crowd when he discussed the perils of marriage.

"But you can make mistakes with people, just look at the divorce rate," he joked.

Along with his late business partner, Charlie Munger, Buffett is known for saying that a person's choice of spouse is one of the most important decisions they'll make in their life.

Buffett briefly commented on the rise of deepfakes and other forms of imitation, calling it a "scary" trend, especially at a time when several countries possess nuclear weapons.

He lifted the crowd's spirits with his final comments. He heralded America's remarkable longevity and lasting appeal as a place to live.

Then he reiterated his faith in the "golden rule," which Quick clarified was the biblical advice to "Do unto others as you would have them do unto you."

"I've never seen anybody unhappy that behaves that way," Buffett said.

Quick ended the conversation to whoops and applause with the words: "Warren Buffett, the chairman of Berkshire Hathaway."