Not necessarily. I’m not sure what the usual Bombus arrangements are, but it is fairly common for males of many species (and females of cuckoo species) to sleep in flowers, often in aggregations (e.g., see the observations in this project). I’ve also occasionally seen females sleeping or waiting out bad weather in flowers, so it doesn’t seem to be outside the range of normal behavior. It may depend on whether one is in the middle of nesting and has to defend one’s space from intruders/other females or not.