This sort of thing add to the perception of American police.
It is true American cops do shoot more people than their counterparts in non gun owning countries. And they can get a bit jumpy until they see what a person is about, which is somewhat understandable given the environment.
The advice to keep your hands in plain sight and don't make quick movements is good. It's very unlikely you'll get shot (as per the stats above) but to help keep everyone calm and happy. It's not really a big imposition.
This probably sounds like weird advice coming from another place. But every place has it's strange things. You have to understand, America is not far removed from it's frontier days. It's always been a fairly violent country. That doesn't mean it's not in general safe, it is for the most part, it's just there are a lot of guns and a fair amount of violence compared to Sweden or some place like that.