[1] https://en.wikipedia.org/wiki/Police_Service_of_Northern_Ire...
[1] https://en.wikipedia.org/wiki/Police_Service_of_Northern_Ire...
As for why they might pull their sidearm in such a case, just ponder the following statistics.
United States: 112 guns per 100 residents.
United Kingdom: 6.6 guns per 100 residents.
The United States has around 5% of the world's population, but 30-50% of the world's civilian owned guns. The gun homicide rate in the US is about 60 times that of the UK.
For one, the numbers I've seen for per-capita are around 88% (2014, I think), not 112%.
However, the number of gun owners is estimated from anywhere between 12-33%. So no, number of guns in the country can't be used as a rationale for the probability that an officer will encounter a gun in a stop. Gun owners are a minority.
From all accounts so far the officer radioed he had a broad nose.
Edit - Here's a Snopes link describing the particulars of the falsehood: http://www.snopes.com/philando-castile-was-not-wanted-for-ar...
"Police who pulled over and killed Philando Castile reported they thought he might have resembled a suspect in an armed robbery case."
He was not stopped over a broken light, police _thought_ he could be armed and dangerous. (I can not judge the validity of their suspicions)