Very good points. It's hard to know what would have happened if the one fellow had not turned around and shouted. Would the bear have barreled right into them?
Re spray and shots, no one uses those, only one-ounce slugs or an even more potent cartridge like this https://www.brennekeusa.com/hunting-ammunition/black-magicr-magnum/. Distances are point blank. My informal line in the sand with a bear that doesn't respond to other deterrents is 10 metres, although it depends on the situation. I've never had to kill a bear. Unfortunately, some travelers have frivolously let polar bears come too close in order to take photos, then shot the bear when it became too inquisitive.
One good thing about travel in the open Arctic is that unlike tree country, or Alaskan subarctic brush country, you tend not to surprise a mom and cubs. I've had all too many scary incidents with polar bears (over a dozen), but in my only close encounter with a mother and cubs, she was very respectful and moved her two cubs off. We then, equally respectfully, shifted our camp 10km away.
No wonder you have tried to understand these animals as much as possible, having survived an encounter like you describe.
Having served in the infantry I also have some understanding of using weapons on an attacking force and even in a well trained user using a firearm to effect, even a shot gun, depends as much on the force as the user. Spray and shots will work at distance on a territorial or predating bear, but on a defensive female it's MUCH closer range and is arguable what time it will buy you and it may not prevent some level of attack. Any weapon you have will need several rounds capacity in quick order. Handguns would need a pretty good level of decisive use at a range close enough an untrained user would be relying on luck to have. The body mass of a bear, it's composition and it's drive makes shooting an attacking animal completely different to hunting one or defense against a human.
That video is very good, but there's no luck involved - the bear stood down. Those guys didn't stand a chance otherwise (well one of them might of, recalling the old joke about not having to run faster than the lion, just faster than the other guy).