No that's not some sort of perverse sexual behaviour but an occasion when "a large group of people assemble (apparently) suddenly in a public place, perform an unusual act for a brief time and then disperse."
The woman who got the "show on the road" (screenshot from YouTube video)
It's a trend that has more than taken off in recent years in towns and cities around the world, and quite often videos find their way on to YouTube where they frequently "go viral".
A recent such example was on November 13 as "unsuspecting shoppers in the food court of Welland's Seaway Mall got a big surprise while enjoying their lunch".
And it was a seasonal one at that as over 100 participants performed the "Hallelujah" chorus from Handel's "Messiah".
As the organisers said on the video (proving they're Canadian?) "Awesome".