Welcome to the Thanksgiving and Christmas seasons.
Great! I'll bet the customers were blown away.
However, the chance of this being a true flash mob is pretty slim. This was a group of trained singers who prepared for, and even choreographed the performance. Did you notice that there was no conductor? Well, putting this together without one takes a lot of coordination. Just the fact that the vocalists were all well trained leads one to believe it's not a flash. The entire production was well rehearsed, everyone knew when to stand and who sang in what order to begin. In the original score there is no solo in the beginning, the whole choir begins on note 1, so the music was arranged for this event. In a true flash mob, there would be no chance to make such arrangements.
It's cool anyway.
You're right - this is no 'flash mob'. It's the Chorus Niagria according to the notes from Alphabet Photography who sponsored it. It's very nicely sung in a rather poor environment for singing. From the looks of the video, it appears that there may be a few people who just joined in for the fun of it.
Like you said - it's cool anyway!
sidebar: always find it amusing that a piece of Easter music has become so linked to Christmas...or for that matter how "Linus & Lucy" got to be a staple of the Christmas genre - both great bits of music, but not having a thing to do with Chirstmas.
It obviously was a choir that rehearsed together. But, I'd say it still counts as a "flash mob" if they communicated to eachother to spontaneously show up there at that particular time. All any flash mob is a collection of folks that show up from a particular forum or Twitter page. Who's to say the choir didn't assemble in response to a tweet or forum post from one of the member's or directors page?
Oh, and Vince Guarldi's is one of my favorite Christmas albums Linus and Lucy is OK. Skating is probably my favorite tune though..