It's supposed to have its origins in rule of the road, but it doesn't follow that nowadays. At least, I'm sure I remember NZ bikes being Left Front. More to the point, there's personal and 'genre' variation, UK road racers following Left Front too (perhaps this dates from the League of Racing Cyclists – was that the name? – with their continental manners in the 1950s, as opposed to the TTers).
But bikes with coaster brake and front lever brake always have the lever on the right. As do motorcycles since the 1970s at least.
And QG's mechanic was rash to put his hand in the spokes before they'd stopped spinning.