We kept walking, hearing more music along the wharf.
Another group of fishermen were standing on a distant boat, saluting each other with drinks (apparently whisky). Closer to us on the pier a family was having a picnic lunch. Next to their table were three musicians playing for them. A woman was grilling fresh fish on a barbecue. It sounded like everyone was having a lot of fun.
Only after coming back home to Sofia did we learn that Sunday was the Saint Day for St. Nicholas, who is the patron saint of the fisherman. That was the reason for the many celebrations, and the music and the bands, and the grilled fish, and even the larger crowds on the streets of Burgas that night.