Criminal copyright infringement requires that the infringer acted for the purpose of commercial advantage or private financial gain. There is a higher threshold for criminal infringement. Singing happy birthday in public would be a civil offence, not a criminal one.
I think the relevant bit, amid the satire, is that restaurants, regardless of size, whose employees are caught singing "Happy Birthday" are hit fiercely by this. Ever wonder why the employees at chains sing something else?
To be a little more specific, there is no risk when a group of friends sing happy birthday to someone they know in a restaurant. However, if a restaurant's staff routinely sings the song to customers, then people will come to that restaurant specifically to receive this service - which is profiting off the song.
