It was surely the most bizarre crisis of the Biden administration: America's top-of-the-line jet fighters being sent up to shoot down, of all things, a balloon – a Chinese spy balloon that was floating across the United States, which had the nation and its politicians in a tizzy.

Now, seven months later, Gen. Mark Milley, chairman of the Joint Chiefs of Staff, tells "CBS News Sunday Morning" the balloon wasn't spying. "The intelligence community, their assessment – and it's a high-confidence assessment – [is] that there was no intelligence collection by that balloon," he said.

So, why was it over the United States? There are various theories, with at least one leading theory that it was blown off-track.

The balloon had been headed toward Hawaii, but the winds at 60,000 feet apparently took over. "Those winds are very high," Milley said. "The particular motor on that aircraft can't go against those winds at that altitude."

The balloon floated over Alaska and Canada, and then down over the lower 48, to Billings, Montana, where photographer Chase Doak, who had studied photojournalism in college, recorded it from his driveway. "I just happened to notice, out of the corner of my eye, a white spot in the sky. I, of course, landed on the most logical explanation, that it was an extra-terrestrial craft!" he laughed. "Took a photo, took a quick video, and then I grabbed a few coworkers just to make sure that I wasn't seeing things, and had them take a look at it."

Martin said, "You'll probably never take a more famous picture."

"No, I don't think I ever will!" Doak said.

He tipped off the Billings Gazette, which got its own picture, and he told anybody who asked they could use his free of charge. "I didn't want to make anything off it," Doak said. "I thought it was a national security issue, and all of America needed to know about it."

As a U-2 spy plane tracked the 200-foot balloon, Secretary of State Antony Blinken called off a crucial trip to China. On February 3 he called China's decision to fly a surveillance balloon over the Continental United States "both unacceptable and irresponsible."

President Joe Biden ordered the Air Force to shoot it down as soon as it reached the Atlantic Ocean.

Col. Brandon Tellez planned the February 4 operation, which was to shoot the balloon down once it was six miles off the coast.

Martin said, "On paper, it looks like this colossal mismatch – one of this country's most sophisticated jet fighters against a balloon with a putt-putt motor. Was it a sure thing?"

"It's a sure thing, no doubt," Tellez replied.

"It would have been an epic fail!"

"Yes sir, it would have been! But if you would've seen that, you know, first shot miss, there would've been three or four right behind it that ended the problem," Tellez said.

But it only took a single missile, which homed in on the heat of the sun reflected off the balloon.

After the Navy raised the wreckage from the bottom of the Atlantic, technical experts discovered the balloon's sensors had never been activated while over the Continental United States.

But by then, the damage to U.S.-China relations had been done. On May 21, President Biden remarked, "This silly balloon that was carrying two freight cars' worth of spying equipment was flying over the United States, and it got shot down, and everything changed in terms of talking to one another."

So, Martin asked, "Bottom line, it was a spy balloon, but it wasn't spying?"

Milley replied, "I would say it was a spy balloon that we know with high degree of certainty got no intelligence, and didn't transmit any intelligence back to China."