If there isn't a writhing, buzzing mass of thousands of bees, it isn't a swarm. There will be no doubt in your mind. Think "basketball made of solid bees clinging to each other."
When I was a kid my folks had a beekeeper who had hives in our backyard. We'd get occasional honey, and dad got his garden and fruit tries well pollinated. Never once was I stung by a bee (wasp yes, once, bees never).
That said, they might not be colony-based honeybees. There's plenty of other (solitary) bee species that it could be, as well as a number of bee-mimic fly species.