When I first saw this video on YouTube, I assumed it was some American mall - didn't realize it took place in a mall here in Ontario! (On a second viewing, I saw the OLC Lotto signs, which gave it away.)
I think we're getting so used to seeing these sorts of things nowadays that we're no longer really surprised, which defeats the purpose. If I was in a food court and people were randomly singing, I would simply have assumed they were some form of street performers. Just like if you walk past a busker on the street you don't think "Gee whiz, that random ordinary man just started juggling chainsaws!" Especially since, by the sounds of the audio, some of them must have been wearing mics.
Also, judging by the waving hands at the end, probably about half of the people in the food court WERE the performers, so that reduces the surprise impact a bit.
I heard they'd been practicing the song for several months before they performed it. Whew!