“If you are stopped for a legal reason...”
The cops had a complaint. We do not know what the complainer said, but I’d bet she (probably a she) said the guy was acting weird and dangerous. Complainers don’t always stick to the facts.
Once the complaint has been made, the cops DO have a legal basis for finding out what is happening.
If the complaing is of an illegal activity, yes you are correct. If the complaing was simply “I saw a man carrying a rifle.” There is no illegal activity and thus no reasonable suspicion and thus no authority to disarm. The only authority is to conduct a consensual encounter.
We do not know what the complaint was. But given how liberals think, I’d bet a large sum of money the complaint was that some guy was acting weird, has a rifle, looks like he may shoot somebody. And the cops in the patrol car just get what the dispatcher tells them, which was probably along the lines of “Report some guy with a gun is acting strange, location XYZ”.
So yes, they do need to stop and talk to the guy, and during that time they do (in Arizona) have the right to disarm anyone nearby.