So if someone calls in to the UK police that there's been a shooting and a murder and the person has a gun, the cops don't show up with weapons and ready to shoot? How does that work?

Sure, police culture is very different, but this is irrelevant.

It’s just false to claim that swatting is a US only phenomenon or a function of police culture.

It is a US-only phenomenon. So far nobody was able to show an example of this happening in other countries.

Why are you making a false statement when you could easily have checked for yourself?

https://www.newstatesman.com/sci-tech/2015/08/swatting-uk-tr...

The article clearly says it was the first such occurrence. Also, it’s not clear this really was swatting, in that nobody was endangered: the police didn’t storm the house.

The word phenomenon implies repeated occurence, not some one-off or rare situation.