The terms Popcorn, Belgian Popcorn or Belgian Northern Soul have been around for a while. I suppose to those NOT in the know it has become more of a confusing selling point, meaning, like many specific sub-genre terms, record dealers use those terms to hawk their gear in more visible/searchable places like ebay™. I'd reckon if most Americans heard Popcorn, without it being called Popcorn, they'd be hearing R&B or "oldies," which they are, of course. However, the specifics of Popcorn are, well...quite specific. Like Shag in the Carolinas, Popcorn as a sound/dances/scene evolved from a specific groove provencial dancers seemed to favor most and it in time grew into it's own thing!!
Belgium, 1970. While most radio stations and discotheques are playing the pop and rock hits of the day, a new venue opens in the small village of Vrasene, near Sint-Niklaas. The place is called The Popcorn and the dj’s play obscure soul records which they slow down in order to create their own sound. A few years later, music lovers and dancers come from all over Belgium, France and The Netherlands to enjoy this unique music. More and more venues start playing this style of music, which they refer to as ‘the Popcorn sound’ or ‘Popcorn Oldies’.
Now, watch this mini-documentary for more details!! And yes, James Brown's The Popcorn LP was the inspiration for the name of The Popcorn club.