I must have mis-read the story. The dude got out of his truck with a knife in his hand. That is justification for the search for weapons (the cop also could have simply shot him dead)...
No, it is not. Not even close.
It is perfectly legal to possess weapons, in nearly all states.
It is one of the things this decision clarified.
Mere possession of weapons is not a cause to stop and search, in most places.
A few states ignore the Second Amendment by making possession of weapons illegal in most public places.